To the best of my knowledge*:
. . . Table Service desserts may only be ordered while seated at the given TS restaurant for the given meal; no 'tokens', no coming back later for dessert.
. . . There has never been any such thing as a token for unused snack credits. You either 'purchase' a snack item or you don't. The credits aren't dated; you can redeem a snack credit at any time during your stay. You can wait until just before you go home, and go get a dozen Rice Crispie Treats all at the same time if you want and if you have that many snack credits 'left over'.
. . . At some Counter Service restaurants, if you wish to include an ice cream (likely the only perishable dessert) with your meal, they may give you some indication - a token, a special mark on your receipt - allowing you to return to that same location within a set amount of time, to get the dessert.