In the festival store, what are the most-desired items that won't disappear by the end of the festival if they haven't been used?

I suspect the avatar items won't disappear but it sounds like the seeds will.

(I'm new and not sure what to buy, but don't expect I'll use it until I know more about the game.)

all consumables directly relating to springfest will become useless at the end of the fest's hard close, and will disappear upon the start of next year's springfest. It is the same for all fests- supplies/consumables (enrichment baskets, fest currency, seeds and all other other growing items) are viable for only one single fest.

Things in the Avatar item section are the only items from the shop that are not part of that consumables category

Cool, thanks for the tip!