Normally lounge access excludes you from a refreshment voucher, but being familiar with that lounge - and its sparse offerings - means I can see you may feel hard done by, particularly if the onward flight is in ET. Furthermore I can't see an easy way for you to get the vouchers since the BA gates are at the other end of the building and past passport control. I imagine there won't be anyone there until about 45 minutes before the flight actually leaves. The best I can suggest is to ask the receptionist to ring BA to see if they will do anything, but it would not surprise me if the answer is no. Your other option is to photo the snacks in the lounge, buy some sarnies outside and bill BA afterwards for them. If you spend less than €10 per head I imagine they would pay up.