For example I seem to always have what everybody needs/wants, from Advil to bobby pins to a deck of cards. What would you call me?
I would just say somebody is ready for any occasion or well-stocked.
I think the simplest term is prepared.
to make yourself or someone else ready and able to deal with a future even
Boy scouts are always prepared and if this person just had 100s of items and was a woman you could go with Mary Poppins.
They are often called as lifesaver.
something or someone which provides help that is badly needed
They might be called a supplier or a ready supplier.
There is a military term called provisioner also.
A friend in need is a friend indeed. If what you need is a year's worth of freeze-dried provisions or enough ammunition to topple the government of a small country, they're probably a prepper.