Something to open a jar with, would be handy for any senior, who doesn't have
alot of strength in their hands. I often found this to be a problem for me manually.
Also the long sticks with a movable clamp on the end to retrieve things from an
upper shelf. Or a step stool with an easy to hold onto bar at the top to hold onto.
Anything that makes life a little bit easier, and safer are all needed by seniors.
If he doesn't have one of those LED lights that fit on the head that might be good, especially if he is working on plumbing or looking down into cabinets and other dark spaces. A LED goose neck lamp would be great too.
Coquavin, is he frail and elderly? The gadgets which make those lives more manageable (large-button phones and calculators, simplified DVD players, electric can openers) would be insulting to someone able to fix up his own house.
Cordless power tools (drill?) and electrically powered hand tools (hammer?) might be good, or a painting tool which resupplied the roller or sprayer without the painter having to return to a tray. Cuts painting time way, way down.
Try a Nintendo DS and a load of games. Before you say that's not a gadget for an elderley person - a LOT of us over 60 play RPGs and puzzles games on the DS - it keeps arthritic hands working AND our brains.
Or you could think about one of those new pocket camcorders - to take pics on holiday or of pets or the grandchildren?