Where did they get all of the gum from?

Ted has a backpack from which he produces several Chocolate Pudding tins

Ted: Here is a treat to make our minor prehistoric pit stop a bit more enjoyable.

The fact that he has enough pudding tins to share is a fair indication that he is prepared with other treats as well and it isn't much of a stretch to imagine that an air-headed high school kid from the 80's would also have several packs of bubble gum in his backpack to share as well.

So where did they get all the gum? From Ted's backpack (which is indeed along for the already crowded ride), and likely before that, the Circle K.

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