Start by picking out your graduation gift bags. You can find them at party stores or online (see resources). Make sure they have the year of the graduation on it. It just doesn't look right without that.
Purchase some stationery sets to go in the graduation gift bags. Most of the graduates will be going away somewhere and even if they aren't some of their friends will be. They can use the stationery to write home or to write to friends who are away at college.
Bake some cookies in the shape of a graduation cap or a diploma. Place five cookies in a plastic bag and close it by tying it with a piece of ribbon. No graduate will turn down homemade cookies and they are very inexpensive to make and include in the gift bags.
Include a scratch off lottery ticket in each bag. You can purchase a ticket for $1 and who knows, one of the graduates may get lucky. This gift is fun and won't take up much room in the bag.
Add a pack of cards to each bag. This could be a set of regular cards or a game such as Uno. This will give the graduates a game to take to college that won't take up much room in their suitcases. You can buy a set of cards at the dollar store so it won't cost much.
Add some office supplies the graduates may need when they go away. This can include pencils, pens, calculators, staples, paperclips, thumb tacks, etc. These supplies are small enough to fit in the gift bag, and very practical.
Finish the bag off by adding some personal items. All of the graduates will be able to use soap, shampoo, razors, laundry detergent, fabric softeners, toothbrushes, toothpaste, etc. no matter where they go after graduation. This will save them from having to spend money on the small stuff so they can save up for their college books.