Hi! I'd recommend physically going into local stores and handing in your CV, and if you don't hear anything back, make sure to go back in multiple times after handing it in (quite a lot of employees do this to see if you're super interested). A lot of places about now will be losing staff due to people leaving for university, so hopefully more places should be hiring, especially for either weekend/evening jobs- so keep looking!
You could try posting on your local facebook community page, to ask for any local jobs that are available, or you could offer babysitting or dog walking services- that sort of thing?
What sort of things are on your CV? Make sure you slightly adapt your CV for each job you apply for (e.g. retail, include the fact you enjoy organising etc.). Include any work experience you've done also
Also, for sixth form please don't stress about getting too much stationery, you really don't need it! Focus on the essentials, lined paper, pens, 3 folders. You can get them super cheap from supermarkets- I'd recommend Tesco. For uniform, definitely buy clothes off vinted/depop, it's a lot more affordable than buying brand new.
I hope this helps 🙂 Best of luck!!