* Single Dice at reasonable prices.
Many retailers forget the importance of dice. At a local (not so friendly game store), he has all of the minis, games, books, etc. in the world and only a handful of chessex dice sets. This is pretty backwards in my view. Sell single dice of all shapes and colors. The displays look nice anyway...
* Singles of D&D minis, magic cards, etc.
Many people don't like buying boosters and would like a selection of single minis/cards. This is something I look for in my game stores.
* A USED section of RPG books
Buying and selling used material at a reasonable price is a third thing I like to see. People don't always want to shell out $30-$35 for a new, mint book, or they might be looking for out of print stuff (D&D 1st and 2nd edition, for instance).
* Snacks and Drinks
This is another important one that many people overlook. I also wouldn't mind some stores selling deodorant alongside the snacks, but that is, of course, optional.