There is so much conflicting advice to be read on the Internet, from avoiding a great long list of things, to eating anything you want. It can scare you silly as well as completely confuse you!! You should certainly not be drinking alcohol whilst you are on medication. It takes a good few weeks to get over an attack, from both the illness and the severe side effects of the medication. So you will feel rough for a bit, but in 10 weeks time you should be feeling very much better. I have had this illness for 17 years and lead a totally normal life, taking part in competitive sport and in general doing anything I want, or my dodgy hip lets me. So life goes on!
HOWEVER, in order to manage the disease you will have to make some food and lifestyle changes. Every healthcare professional will tell you to follow a healthy diet, containing plenty of fibre (soluble kind), as treatment for anything from earache to ingrowing toenails. Whilst you are still on medication then in recovery, you should follow a low residue diet (no fibre), then slowly re-introduce fibre as you improve. Suggest you look up the post DiviDiners. Have you been following a recommended diet for people with no gall bladder? One thing most of us do is keep a food diary and note anything we eat or drink which causes symptoms. That way we can work out what affects us individually. There is no hard and fast rule, as we all react differently. For example I can't take gluten or full fat. For others it could be red meat, nuts, seeds, corn, dairy or any combination. As you say if you avoid everything anyone has ever had a problem with, life would be miserable. It's a case of trial and error.
The secret is small, healthy, well cooked meals, well chewed, and no overloading your insides. On the positive side, you may loose a few of the excess pounds. I happily have the odd glass of wine or liqueur, with no ill effects, but I am not a drinker. A few weeks down the road you could try a small amount of beer to see what happens. If you do react, then at least you will know. This is what most people do with things they like, but are cautious of taking.
I think your main consideration will be to get your friends onside. A lot of people at first are scared to do anything, go anywhere, and just lock themselves away. Sooner or later you just have to tell yourself to get on with life - you are not going to let the disease rule it. Tell them you can't eat/drink as you used to, and tell them clearly, if they start nagging you, you don't want to spoil the outing for them or yourself by being ill. But you can still go and enjoy the festival by knowing your limits and sticking to them.
Someone else might have more information regarding alcohol and DD, I hope.