So today is Tuesday and I have a cake that has to be done by this thursday. Can I make a small purse out of RKT tonight, cover with buttercreme and then with fondant? Will it still be fresh for the party on thursday and where should I store it?

Any suggestions, ideas and comments are welcome

It will definitely be good. I typically made my rice krispy "cakes" up to a week in advance depending on my schedule and other cakes to be done. Rice krispy treats last awhile anyway (well stay good awhile, actually lasting in this house is another story). Then once covered with buttercream and fondant they're sealed from the elements (just like a cake)

I would keep it in a cake box, don't put it in an air tight container, all that moisture could reck havoc with fondant.