Tesco helped me pay for my driving lessons, buy my first/second/third car and helped me through Uni. All from working in the PFS on weekends while studying in the week.
With A levels and experience from working there why not become a team leader (they are on a tidy sum of money). Might give you some people management skills and show you're trustworthy?
But getting an admin job at a local flying center would be much better, all you'll hear on this forum is 'networking' and that is possibly the biggest asset you can have after gaining your fATPL. Getting to know the CFI and fellow FI's will put you in good stead should you wish to go down the FI route.
As said above, you might be better off in staying with 1 place to gain your CPL & ME-IR. I'll be going to US for my PPL due to the amount of time it takes to gain a PPL in the UK (weathers fault).