How would you feel if your boss paid you this month with Broccoli, Quorn and vitamin supplements, unless you are a big donor that might influence genuine outcomes for those rough sleepers and you feel inclined to give a couple of quid, just give it without prejudice.
I am inclined to give a couple of quid, but I find it slightly odd that anyone that wishes to give a couple of quid to rough sleepers then demand that as the donor they should then demand that they spend it 'wisely'.
Personally I just hope it helps a little, whether its spent on food, vitamins...