Ive done the local gardening club a few times but i'm not a confident speaker so dont really enjoy doing demos, I wouldnt do a basket if i were you as they'll probably want to do their own and not buy yours, even though they are over 50 you will be surprised how they enjoy something different, try and think of what you have in the shop that you wouldnt mind getting rid of in the way of pots etc and what you could do with them that people would want to have a go at and come and buy them from you. I didnt use too many flowers because it was the gardening club and they dont buy flowers really, just whats in their garden but i did use quite a few sundry bits so they would buy them, wires, butterflies etc. One thing that did go down quite well was the vase that i filled with fruit.....cranberries i used cause it was around xmas but you could also slice fruit like lemon, limes, oranges and put couple of large leaves and a few anthuriums or something out the top, you could do that for a side line not to raffle maybe. The other thing they liked was the birds nest design with bendy twigs, i used dogswood ivy etc, but this taken quite a long time so had to half do the design and just told them what i had done, a bird cage might be a good idea too. Anyway, whatever you decide, good luck with it and remember to know the latin names of everything you're using, cause theres always a smart ass in the audience. Dont forget to take a selection of what you are using so that you can sell stuff afterwards