I'd buy fabric if that is hard to get or expensive in the UK.
As for the red wonder clips. I remember taking a binding workshop and the nationally known teacher said jokingly: 'you only really need just one and keep moving it, then share the rest with 9 friends." I usually only use 2. So if you buy more ... share.
When I have to do a lot of HST I tend to use Thangles the most. Less squaring up and things go quicker for me that way.
I expect you can get most rulers in the UK. My favorite specialty ruler is the 8 inch Bias Square [up] ruler by That Patchwork Place.
Rotary blades and maybe try out rotary cutters if there isn't much choice in the UK.
From my LQS I buy a 100 needle box of sewing machine needles. You might want to compare the prices on those also.