My mum did a good fruit flan recently - she used grilled apricots but strawbs would also be good. V simple (because mostly bought):
1 Go directly to M&S 2 Buy 1 pastry flan case (they do a buttery pastry one - v crisp and yummy) 3 Buy 1 tub of their creme patissiere 4. Slap that together and then arrange your halved strawberries artfully on the top. 5. Et voila!
Honesty bucket is a lovely and trusting idea but I think you would get far more by charging for each item individually. even if each item is only 50p or a £1, for example if someone was buying 8 items (say family of 4 buy drink and snack each) that would be £8, but if you had an honesty bucket they might just put a fiver, and not that thats not generous, but YSWIM hopefully!