Hi
The obvious choices are
NAS squash drinks, any flavour
NAS Crusha in Milk only the strawberry one though not the chocolate one.
Low Calorie Hot Chocolate like Cadbury options
Low calorie instant lemon tea
Fresh Orange mixed 50/50 with water
Plain old water bottled or out the tap if bottled still only.
Basically anything that will not make you dump, no sugar, no fiz and no alcohol.
You also don't want to tempt drinking anything that should make you dump only to find out you are one of those people that don't dump, because that will make things much harder as far as weightloss is concerned. If you find that drinking alcohol and eating chocolate dosn't make you ill you are far more likely to consume them and that could sabotage you weightloss, and in some cases that has lead to the surgery being totally waisted. You would be surprised just how much chocolate can be consumed in a day, even with a bypass, because it mets in the mouth and is very easy to swalllow.
50% of the effect of weightloss surgery is down to aversion therapy, don't eat it as it might make you I'll, if you lose the aversion you lose the battle.
Paul