The closest thing I can think of is menstrual cramps, but they're a lot more intense. Have you ever coughed the day after doing a bunch of abdominal work? That's sort of similar as well. Back labour (I only had a very small bit of this) feels like low back/kidney pain.
The best analogy I heard for what "pushing contractions" would feel like is it's like "throwing up downwards".
I think it's different for every woman though. For me, I had contractions I had to cope with for about 3 weeks before I actually went into labour - the labour contractions were much more intense. My actual labour with dd lasted about 4.5 hours before pushing, but time really seemed to go by fast and it felt a lot shorter. Also, for me labour wasn't so much painful as it was very intense - it was hard work.
Really, though, if you don't recognized labour the worst case scenario is that you won't know you're in labour, which would mean the contractions are easy to cope with
I'm sort of hoping that's what happens to me this time around - I'd love to give birth before I realize I'm in labour - how easy would THAT be!?
My contractions definitely were easier to cope with than gas pains (I have/had IBS so I've had my fair share of those). And waaaaaay less painful than the super-full bladder I had for the ultrasound with dd.