I don't think someone will have a 100% answer to your question. You just have to do your own research, locally by driving around or something and see what people are buying, how much are they spending per item, what items sell the most of, etc. You just need to do a market research. Any business is always a risk, it's those who is willing to take the risk first may become filty rich or..fail but gain tons of experience.
@ Hoppy's_ParadICE regarding stands in Florida. Part of the issue is how tough Florida is on vendors. The Commissary requirement, the Food Manager's testing and various other licensing make it tough to just go and set up carts.IMO. They don't make it easy.
Shave Ice Tips and Pointers
This section will tell you the basics on how to make a good Hawaiian shave ice! Please feel free to ask questions you may have regarding local shave ice and shave ice in general.