I at least pinch the tires, or bounce the bike lightly, every time I get on it. Bouncing the bike identifies parts and accessories getting loose, too. Like those above, I typically top off air every week, usually 5 or 10 psi on a road bike. If it's more than that, I'll look for a leak when I have time. Definitely get a floor pump with gauge at home, and a frame or pack pump for the bike.

As already said, changing a tire should be routine for an active cyclist. In my commuting days, I'd get several flats a month, and I could do a front wheel in just over five minutes, rear in ten. To this day, I always leave an extra ten minutes when cycling to meet someone, in case of a flat tire. If you do it right, have normal strength, and depending on your tire and tube, you may not even need any tools, especially on a MTB. Carry a tube and pump, and a patch kit in case the spare also picks up a thorn before you get home. Or both tires get flat in the same patch of thorns.