I dabble in reselling too. The past two years i was really involved in it, earning around £150-200 extra a month. Not so much this year, with car boot sales being called off and charity shops being closed.
Hoping to get back into it next year! Covid permitting.
I do often complete surveys online, whilst this doesn’t earn too much an extra £20-£30 a month helps out and adds to my fun money for the month.
I’ve tried matched betting, heavily involved two years ago whilst saving for my house deposit. Earned around £500 off it. Before I realised how much I despised it and found it so boring! It can be a very good earner though if done correctly.