Ok so there are millions of these things nowadays, but I can heartily recommend Google Opinion Rewards for Android. It's an official Google app, and every couple of days it'll throw a two or three question survey at you based on places you've been.

It'll literally be, 'Have you been to this shop. When did you go? Rate it out of five' and that's it. You get pennies for each one, anything between 5p and 49p I think was my highest.

It all adds up though. In around 18 months of use I've made over £60 in Google Play store credit. I know that sounds like nothing, but it's paid for every premium game I've wanted on my phone in all that time, just for clicking the odd thing every now and then.

Thought I'd give a heads up, because in a sea of dodgy scam apps, this one is actually worth having.

I've been using Google Play Rewards since late 2013 and can verify that 95% of the questions I'm asked are "Did you go to the grocery store today? Did you buy anything?" and I get a few cents each time. According to the in-app reward history, I've earned $156.81 USD since I started using it, all of which has gone toward buying movies, apps, and in-app purchases for various games I've played over the years. Almost never had to spend a cent of my own money for premium apps/games.