Home Repairs Party
I don't know that I'd do this one unless it's coed, but it is considered a traditional shower. You would suggest that the guests bring things one fixes up a house or yard with. Gardening gloves, rakes, paint brushes, a drill, things like that.
You could also bring books on the subject, a discount coupon from a handyman, a gift certificate to a paint store, or have one of those ladies who sells home decorating out of a van come and do a demo (pay her on the side and be clear about whether or not she can pitch her wares during the party).
For food, you could use paint-roller pans (new, clean ones!) as serving dishes, have everyone wear a painter's cap with his or her name on it (a cheap, easy way to learn new names!), and have everyone dress in overalls. Or you could have the shower at the bride-to-be's new house and everyone could really pitch in! Send the guests home with garden trowels or paint brushes tied with ribbons.
Perfect invitations would, of course, be to buy a really inexpensive set of aluminum pocket screwdrivers—those little ones not bigger than 3 inches, with brightly colored plastic handles. You could tie them securely to sturdy paper invitations with a bit of twine or wire, so they won't slip during mailing and make holes in the envelope or stab the mailman! Short of that, what about mailing cheap plastic switch-plate covers with printed invitations glued to the inside?