I AirBnB out my second bedroom and have done a bit of Uber driving.
For AirBnB, I have probably made close to $5000 in the last year. It basically makes up for not having a full time roommate for a two bedroom apartment. On top of that, I have an arrangement where a coworker stays with me during the week, I shut down AirBnB Monday through Thursday night and he pays me $150 a week. So I've made an extra $2000 over the past 4 months doing that too.
For Uber, I made maybe $1500 over the course of two months doing it a night or two a week. Gas probably takes ~$150 out of that and then there is additional mileage on my car, but it wasn't substantial. Living in a college town meant there were pretty consistent surges for 3-4 hours on Friday/Saturday and you could make bank fast... plus it was kind of fun since I didn't have any bad incidents. I wouldn't recommend it in most situations though. Also I felt morally bankrupt driving for Uber, but the town doesn't have Lyft yet.