Buy it over there it'll be cheaper. I can't understand why anyone buys all that stuff in the first place instead of cooking their own food, not at UK prices anyway it's ridiculously expensive for what it is.
Solar chargers were the go to when battery packs were hellishly expensive.
battery packs, powerful ones, are now cheap and work at night too. Mine will recharge my phone and Satmap a number of times each. Smaller, very light ones, will charge a phone once or use for some usb lights in the tent.
And how are you going to recharge it? You're a Summer car camper. I've been away for anything up to 4 weeks without access to mains and I don't stay on campsites I avoid them wherever possible. I've never needed to recharge a battery at night funnily enough. I charge my batteries during the day so I can swap them around when I need to. It's also inefficient using a battery to charge a battery, all the more reason to connect it directly to a solar panel.