Plaid Cupcake - Here is an approach.
Figure out how much your expenses will be (booth fee, hotel if any, gas, car rental, table rental etc.). Take the total amount and times it by 5. This is the retail dollar amount you should aim to bring with you. I do it this way because I know I need to first cover my expenses and second bring in profit. I times it by 5 because I know that my mark up per item is 2 - 3 times the cost of my item and that the greater the selection you have the more you will sell.
Also, remember you may only sell 30% of what you bring, if you sold that amount would it cover your expenses? Would you make a profit? The stronger your selection is the more you will sell.
At these events there will always be someone who is interested in your product, it may not be every person. But when they do stop by your booth you want to make sure you have enough options that they will bite on at least one or two things.
I know this may sound a little odd, but it isn't just about having enough inventory so that you don't run out it's about covering expenses and making some money!
Good luck.
