You can do useful things, completely Core, with a well-selected familiar. Really. At low-levels, at least.
Bat familiar: Very small, put it inside your clothing, where it sleeps while you adventure. Your clothing is attended (by you), so you take the consequences of anything that attempts to get to your familiar must get through you first (familiar has total cover, so can't be targetted by all but a handful of effects; you're attending your clothing, so except for a handful of effects and natural-1's on saves, you take any damage your clothing otherwise would - like, say, a Burning Hands spell you get caught in). Why a bat? Well, it's got Blindsense, it can sleep during the day, and it doesn't need to rest and regain spells. It's really, really hard to hide from blindsense (Incorporeal, certain non-core feats). Sure, it's only Blindsense-20, so someone with a bow can still give you a nasty surprise, but it's also got a really good Listen score. Taking 10, the move Silently DC to keep a bat from hearing you is 18. You can get a reasonable chance of beating that at low levels.
Owl: Same as the bat, really, although instead of blindsense, it's got a Listen check of +16, and a Spot check of +8 (with a +8 racial bonus in areas of shadowy illunination - like, say, at night, when you're sleeping).
Hard to beat a rat for overall stealth - Hide +16, Move Silently +12;also has a climb and swim speed, so can get around most obstacles. Mind you, a Toad with a Silence spell can beat the rat for overall stealth... but that requires a 2nd level Clerical spell, and the toad has a move of 5.
And to top it off, familiars are intelligent. By default, they understand common, even if they can't speak it. You can tell your familiar to wake you if anything potentially dangerous comes by.