Ayumi H. answered 05/24/19
Native Japanese Speaker with teaching and business experiences
In the example you brought up here, this に means “and” . The person is checking to see if he has everything he is supposed to take with him in his bag.
So, it could also be simply said バンテージ、タオル just like a listing of items.
In an informal conversation among friends and family, “に” is often used instead of “と” when you are listing three or more things. Also, he might be thinking and reconfirming (in his head )about what he is supposed to take as he is checking, which case “ に”is more natural to use “に”.