In the place where you buy coffee there is a shopping bag with drinks and avatars are they just avatars..

Once you buy a fancy drink or a portrait with your tip collection, you will always have it available to choose from in your game. So if you use your tips to buy tea, thereafter you will always have an option of choosing tea or the original coffee when serving drinks. Similarly, if you buy a portrait, thereafter you will always have that avatar to choose from in your avatar list.

Drinks and avatars are cosmetic only and give no game benefit. Once purchased they are a permanent selection in your game. For example, once you use your tip money to buy tea, your will then always be able to select either tea or the original coffee to serve.