When I was 15 years old, my grandfather gave me a really nice socket set for my birthday. He's been dead for 20 years now, but I still have that socket set and I use it all the time. Whenever I use it, I think about him -- my point being, good tools make a nice gift that can last a very long time. If your father is the kind of guy who fixes things around the house, tools are always nice. Here are some ideas:
On that last one, is a grill really a tool? Yes. Of course it is.
*Go out in the garage and see how many of his bits are missing from the case. If it is more than two, a nice new set of bits is a great gift.
**Ditto the advice on drill bits.