Because Bilbo wanted to sneak away from the camp to go see the Dale men, and he wanted to do it in secret.
Perhaps the question would be "who does Bilbo accompany on a trip." Bilbo travels with Gandalf the wizard and thirteen dwarves: Thorin Oakenshield (their leader), Dwalin, Balin, Gloin, Oin, Dori, Ori, Nori, Bifur, Bofur, Bombur, Fili, and Kili. This not including ponies.
Bilbo went on an adventure with the thirteen dwarves, Fili, Kili, Balin, Dwalin, Dori, Nori, Ori, Oin, Gloin, Bifur, Bofur, Bombur, and Thorin Oakenshield, and Gandalf the Wizard was with them some of the time, too.
The Hobbit named Bilbo was too slow during their adventure to get back their treasure, so all the dwarves carried him in turn, especially Bombur.
Gandalf, Fili, Kili, Bombur, Bofur, Bifur, Oin, Gloin, Balin, Dwalin, Dori, Nori, Ori, and Thorin Oakenshield.
Bilbo offered to take Bombur's turn keeping watch, and when Bombur was in bed, Bilbo slipped on his ring, thus becoming invisible, and quietly climbed down a rope that he tied.
Bilbo talks Bombur into taking a rest while he takes the watch for him. He snuck into the elven-king's camp using his ring. When he returns he wakes Bombur so he could finish his watch.
Because Bilbo wanted to sneak away from the camp to go see the Dale men, and he wanted to do it in secret.
When the dwarves and Bilbo are trying to cross an enchanted river, Bombur slips into the water and falls into an enchanted sleep, and he doesn't wake up for a long time.
Bombur carries him... but he doesn't enjoy it because he is so fat :)
There are thirteen dwarves in the Company of Bilbo Baggins, not two. They are: Nori Dori Ori Dwalin Balin Bifur Bofur Bombur Kili Fili Oin Gloin Thorin
Perhaps the question would be "who does Bilbo accompany on a trip." Bilbo travels with Gandalf the wizard and thirteen dwarves: Thorin Oakenshield (their leader), Dwalin, Balin, Gloin, Oin, Dori, Ori, Nori, Bifur, Bofur, Bombur, Fili, and Kili. This not including ponies.
Bilbo went on an adventure with the thirteen dwarves, Fili, Kili, Balin, Dwalin, Dori, Nori, Ori, Oin, Gloin, Bifur, Bofur, Bombur, and Thorin Oakenshield, and Gandalf the Wizard was with them some of the time, too.
The Hobbit named Bilbo was too slow during their adventure to get back their treasure, so all the dwarves carried him in turn, especially Bombur.
Gandalf, Fili, Kili, Bombur, Bofur, Bifur, Oin, Gloin, Balin, Dwalin, Dori, Nori, Ori, and Thorin Oakenshield.
Thirteen. Their names are Dwalin, Balin, Thorin, Ori, Dori, Nori, Fili, Kili, Bifur, Bofur, Bombur, Oin and Gloin.
In order: bilbo, gandalf, dwalin, balin, kili, fili, dori, ori, nori, oin, gloin, bifur, bofur, bombur, thorin oakenshield.