It’s absolutely appalling you are expected to shell out this much. Your hotel and trains should be booked for you in advance, and if you don’t have a company card then you should get a cash advance for food.
I would really talk to HR. This sounds like your accounts department letting you cash flow them, or just being idle (they always hate cash advances). But failing that you can get a card like Vanquis if you have a low ish rating, as long as you pay it off it’s fine.
Anyway, for me it’s Moma porridge sachets, tins of tuna with ring pulls, fruit, salad, tomatoes, bread cheese, ham, humous, those packets of pre-made lentils.
I’d probably get couscous sachets and cuppa soups to have something hot at night. You can boil eggs in the kettle if you want.
If it’s a cheap hotel they might have a guest microwave in which case you are golden.
They will give you crockery and cutlery.