I think the reading idea is a great one. However, we tend to be very cautious as to how much "game" time we allow on GameBoys and Nintendo, etc.,
What we do with the older children is give them each a list (part of the bigger grocery list) and they search the store for that item, bring it back to the cart and mark the price (the best priced they can find) on their list. They LOVE it when there are coupons and they have learned to read the coupon parameters very carefully! LOL <img src="/images/graemlins/smile.gif" alt="" />
We enjoy giving them "quests" for the lowest priced item or finding the best "deal" - also, we sometimes give them a "budget" and have them find items for one dinner. They enjoy the adventure of planning a meal on their own and trying to outdo each other in creativity and price! Plus, they learn

some Math skills along the way.
There are a few items that my husband insists he can ONLY consume in brandname, otherwise the kids see it as a scavenger hunt! If there is only one child along for the ride, they usually read or we take along the trivia cards for the cart trip!