In this era, movies come out in a few months (I grew up on VHS, where you had to wait years before a movie became available to open... and you had to rewind the tapes!). I didn't see it in the theaters, because what it would have cost me to see it there, I could just own the movie instead.
The movie goes back 9 years previous, where Molly (Andy's little sister) gives away some of her unwanted things, which includes her whole Bo Peep lamp stand. Bo comes to terms with Molly outgrowing her, and for a moment Woody is tempted to go with her, but changes his mind when he hears how upset Andy is when he can't find him.
A montage of the passing years shows Andy giving his toys to Bonnie, and Bonnie is about to enter kindergarten. However, Bonnie isn't really interested in playing with Woody anymore and he spends most of the time in the closet. Woody goes with Bonnie to school when he sees how upset she is. At school, during a craft activity, Woody helps a shy Bonnie adjust by getting things out of the classroom wastebasket for her craft. She makes a toy out of a plastic spork and names it Forky.
Forky becomes her new favorite toy, but because it's an actual spork, Forky doesn't realize that it's now a toy, and instead spends all its time trying to get back in trash cans.
The family goes on a roadtrip, with Dad renting an RV camper. Another montage is shown of Forky trying to throw himself into trash cans, with Woody constantly retrieving him or preventing him. Eventually, Forky manages to jump out of the back window of the RV and Woody chases after him.
On their trail to the next rest stop that the family are going to, Woody and Forky bond over Woody sharing with him his life as Andy's toy. Forky finally understands that Bonnie made him into a toy because of her love even though he's a throwaway utensil.
As they come to town, Woody sees silhouette patterns from Bo's lamp. It's inside of an antique store, so he and Forky goes in to investigate. Bo isn't there, but they encounter a doll named Gabby Gabby and a ventriloquist dummy, who's pushing Gabby in a pram.
Gabby and Woody are classic 50's era toys, and have the same voice box. Gabby was a defective manufacturer's toy right out of the box, so she's never had a kid. She dreams of being the shop owner's granddaughter, Harmony's, toy. Whereas Gabby's voice box is removable, Woody's is sewn in.
Woody manages to escape by pulling his voice string which catches the attention of Harmony, but Forky is left behind. Harmony takes Woody to the park where he escapes, but as he's leaving, he sees Bo's set of sheeps and follows them. He is found by one of the summer camp kids in the park. The kid picks Woody up with one hand, and in her other hand she has Bo Peep - before quickly discarding them to play on the swings.
Woody and Bo are reunited and catches up with each other. Bo has been a "lost toy" for 7 years. She was in the antique store herself before escaping. Her sheeps now have drawings and stickers on their sides, and Bo herself looks different too. She lost her bonnet and the top part of her pink dress, and one of her arms is broken - held together by tape.
Woody convinces Bo to help him retrieve Forky by bringing up what Bo use to mean to Molly. He also meets one of her new friends, who rides in an electronic skunk with her - police officer Giggle McDimples. Giggle is one of those mini toys that comes with its own complete set (probably modeled after the Polly Pocket toys).
Meanwhile, Buzz, thinking that his voice box is his "inner voice" that Woody was telling him about (Woody had meant his conscience), starts pressing his voice button to figure out what to do. Coincidentally, his voice box phrases gives him good ideas to help him along. Buzz goes searching for Woody and finds him and Bo as they're getting ready to go to the antique store. Buzz had also encountered two attached carnival plush toys (a yellow duck and a teal bunny), who also tags along on the rescue mission with the hope of becoming part of Bonnie's toys.
Gabby tricks the naive Forky into telling her about Woody, which he knows so much about because of their long walk. Gabby shows Forky her accompanied toy book, which shows her and a little girl having a tea party. Gabby imagines that the little girl is Harmony.
The toys make it back to the shop, where they encounter Gabby, and once again Forky is left behind. The rest of the toys, including Buzz, tells Woody that Bonnie will get over it, but Woody refuses. Woody is surrounded again, but Gabby explains to him how she's never had a chance to experience what he did with Andy.
Woody agrees to give her his voice box for Forky. Bonnie, by chance, had left her backpack in the shop when her and Mom were in there momentarily. The rest of the toys in the RV are able to alert Bonnie about her backpack, so they go back to retrieve it.
Woody and Forky have their chance, but Forky is mesmerized by what he Hope's is Harmony finally being Gabby's kid - but Harmony discards her without interest. Woody gets Forky back with Bonnie, telling him to let Buzz and the other toys know where to meet them at the carnival (by the carousel). Woody convinces Gabby to go with him and be one of Bonnie's toy.
As they are heading to the carousel, Gabby sees a lost girl. She feels that she can finally have a kid with the lost girl. Ducky and Bunny rolls a baseball towards Gabby to get the girl's attention. She sees Gabby and picks her up. The lost girl sees a female police officer and tells her she's lost. She's reunited with her parents and Gabby finally gets a kid.
The toys in the RV has forced Dad to drive into the carnival through incorrect GPS directions and pressing on the pedal, where he's eventually pulled over by the police. At the carnival though, Woody decides to stay with Bo, realizing that he doesn't have the same value to Bonnie as he did to Andy. Instead, he decides to become a lost toy with Bo, Duke Caboom, Ducky and Bunny.
Okay, I wasn't too crazy about this one. This is one of those franchises where they should have quit while they were ahead (ex. Indiana Jones and the Kingdom of the Crystal Skull). TS3 was the perfect ending, Andy goes to college, and now they've been rehomed to a new kid. There's even a hidden PSA in the plot for adults to donate unwanted toys. This was really lacking though (usually what happens when you beat a horse to death by milking the franchise).
I do love that Bo is so strong and independent in this movie. A great Disney role model for girls, and not the usual damsel in distress like the classic Disney princess movies. She actually rescues and saves Woody instead.
Woody giving away his voice box is the ultimate sacrifice for him as a toy. As even Gabby mentions, Woody is in excellent condition for a 1950's era toys (and it's why Al steals him in TS2), so him losing his voice box is essentially the same as Bo losing half of her outfit, her lamp stand, her sheeps getting drawn on, and her arm being broken. They really are lost toys now. Throughout the movie, I couldn't help but think - you guys should have stayed in Andy's freaking attic!!!
See, Woody was clearly Andy's dad's toy. If you remember in TS2, Mom tells Al that she can't sell Woody to him because it's been in the family for years. In TS3, Woody tells the toys that they'll go up in storage to the attic until one day when Andy has kids of his own... I'm just saying, in Toy Story world, Woody and the gang would have done well to stay with Andy's family (even if just in the attic); and instead of TS4 with Bonnie, they should have done a plot where Andy has a son/daughter and the toys finally comes out of the attic.