I have a fairly big expenses bill for my job, I don't have a float either. But expenses are surely supposed to be for stuff that are unavoidable costs of the job but are not routine?

If I have to go to a unplanned lunch with clients after a meeting or something, I'll pay that myself and claim it back as 'client entertaining' on expenses. It isn't a routine part of the job and believe me, I wouldn't be doing it if it wasn't for the job, so why should I fund that out of my pocket?

I get it for things like that, that's fine.

But if my employer started telling me I should buying things that are crucial to completing my job, for example material samples, software licenses etc etc I'd tell them to bugger off.

And that's why these things are either sorted for me, or they give me a company credit card to buy them with.

If OP is routinely buying things that a crucial to the job, surely they should be given a card? Their employer has no right to expect OP to fund the things crucial to the job, when it becomes the routine asking OP to use their own money to fund the business is unreasonable.