I haven't worked there but places like the Co-op are good. My friend makes like £6.40 an hour and he is 16, that is really good to be honest.
I work at WHSmith (only started a week ago) and it is okay, £4.80 an hour and customers don't seem to be really annoying or anything.
unfortunately, if you are a teenager like me, it won't be that easy to find a job anyway.. I applied to maybe 30 places before WHSmith