Belly Bag is a major character in the series Uncle Grandpa. He is a magical fanny pack which has infinite space and contains all of Uncle Grandpa's supplies. He is also Uncle Grandpa's best friend. He has appeared in every episode, since Uncle Grandpa takes him with him pretty much everywhere he goes. His eyes are the buttons on Uncle Grandpa's suspenders, which is confirmed in the episode Funny Face when he cries about Mr. Gus being upset with the gang. He is voiced by Eric Bauza.
Belly Bag is a red fanny pack with buttons as his eyes and zipper as his mouth. He has two straps on his sides that serve as his arms and/or legs and he has two silver buckles on the ends of his straps.
Belly Bag's personality is a complex mixture of willingness to help and support his friends, a voice of reason, sarcasm, and jokes. As seen throughout episodes, he is always there to help Uncle Grandpa out with his endeavors. However, Belly Bag sometimes realizes that Uncle Grandpa doesn't always do the right thing, so he tries his best to steer him in the right direction even if it doesn't always work. Belly Bag is also EXTREMELY sarcastic. His sarcasm is especially shown in Funny Face (toward Mr. Gus about why he wasn't invited to the Funny Face party), Uncle Grandpa Ate My Homework (toward Dennis in response to Dennis's sarcasm toward Uncle Grandpa), Shorts (toward Uncle Grandpa in regards to him destroying an orphanage), Leg Wrestler (making a sarcastic joke about Uncle Grandpa and Mr. Gus being all tied up in the match), and Board Game Night (in response to his lousy dice roll). Despite his constant sarcasm, he's also constantly explaining himself (shown in Uncle Grandpa Ate My Homework and Board Game Night) and constantly backing down if ignored or told to be quiet (shown in Nickname, Driver's Test, and Shorts). He also seems to flirt quite a bit, though his flirting is a bit awkward and sometimes creepy (good example of this would be in Tiger Trails where he asks "What's stoppin' ya?" in a flirtatious manner in response to when Uncle Grandpa says "I could just kiss you!". Another good example is in Jorts when he oggles Mr. Gus's jorts with Giant Realistic Flying Tiger).
Uncle Grandpa - Belly Bag and Uncle Grandpa are best friends and the two of them have never been seen without each other. Uncle Grandpa is the one who is seen interacting the most with Belly Bag and spending the most time with him. Whenever Uncle Grandpa needs something, he just reaches into Belly Bag and gets it out of him.
Mr. Gus - Mr. Gus and Belly Bag don't interact with each other much in the show, but in the episode "Uncle Grandpa Sitter", Belly Bag was seen leaving Uncle Grandpa to go have ice cream with him, implying that they are good friends.
Pizza Steve - Pizza Steve and Belly Bag are friends. They do not interact with each other that much, but they were making funny faces in the episode "Funny Face" and they were having ice cream together in the episode "Uncle Grandpa Sitter" without Uncle Grandpa. Belly Bag, however, has a tendency to spit sarcasm out at him (as seen in the Board Game Night short when he said "Sorry Buddy" when Pizza Steve got hit with 3 kids, a wife, and a mortgage).
Giant Realistic Flying Tiger - Giant Realistic Flying Tiger and Belly Bag are friends but they don't do much together. However, Belly Bag was seen having ice cream with Giant Realistic Flying Tiger in the episode "Uncle Grandpa Sitter" and they were seen making funny faces together in the episode "Funny Face".