Heh 
There are online grocery stores which seem to accept most card types, but I'm not sure what they'd think about a foreign card. (Might also cause your own bank to panic that the card is being used in the UK.) Probably not worth the potential hassle. But thanks for the thought!
Plus I would need to know your address which I'm sure you don't want to start handing out. The best way will be to paypal you some cash and you can go pick it out yourself 
But right now I'm a little low on funds so in a few months, expect a PM from me 
I'm serious... get a paypal account setup and ready! 
BTW, what does a case of beer go for in the UK(or whatever kind of drink you prefer)?
Well, I won't say no, but you don't have to, especially if you're low on funds.
A case of beer is about £10-£20 (GBP), depending on size.
(I should really stop using/linking to Tesco, after their support of the News of the World to the bitter end, but I haven't bought shopping online since then and haven't gotten around to checking out the alternatives.)