I would not recommend any alcohol be taken during the time you are on Accutane. Accutane can cause an elevation in liver enzymes and I would not compound the problem with alcohol.
Also, exercise would be fine but heavy exercise should be avoided. When I have placed athletes on Accutane I use a lower dosage and extend the period that the patient is on the drug..instead of 4 months I chose 6. The final result ( permanent clearing) depends on dosage not time frame. I had one patient, a triathlete, who still suffers knee pain after a course of Accutane. (Was treated by another dermatologist for whom she has very bitter words). So, i your case, if you make sure your exercise is not too vigorous you should be all right. Minor muscle aches you shold be able to tolerate, but anything severe like the feeling of a bad charleyhorse, you should have the medicine discontinued. Any back or joint pain, and I feel Accutane should be discontinued.
Vitamin A supplementation is a bad idea. The amount in a multivitamin would be fine but any other suplementation is not a good idea. Accutane is a Vitamin A derivative and the cummulative dosage of a supplement and Accutane could cause toxicity.
One piece of advice. If you have any problem at all, plese let your dermatologist know.