Hmm... My first thought is to wish for power and immortality but would that really be that great? You risk the chance of coming to a point where existence just bores you to death.
You'd be like the Q living in your metaphorical roadhouse on an empty highway doing nothing. The road stretches for miles in either direction but you don't go anywhere because you've done everything there is to do, seen everything there is to see, and learned everything there is to learn. On the upside, you can pester Picard and humanity in general as if they were your pet.