It's not actually really come up fortunately, but we have an agreement that we have £X allowance a month for our own spending. We don't then need to justify what can come out of that allowance, and if we need to cut back on that spending it will be a general cut back not "spend less on beer" specifically.

Obviously join expenses like meals out would still need to be cut back too, but we're at least doing those together in the first place.