Whitewater - A bigger drum will help.

Also, as silly as this may seem, exercising the right arm to build maximum strength while keeping it limber, loose and relaxed. One effective thing I have students do is do EVERYTHING they can with the hand that is either weaker, or the hand or arm they are having tension problems with - open doors, turn water faucets, etc., and pay attention to the amount of pressure they are using to do so.

To build raw strength (to make one hand as strong as the other), simply do EVERYTHING possible with that hand. To build endurance, extend your arm straight from the shoulder with your palm facing up - nice and relaxed. Hold it there for one minute - piece of cake right? Try it. Don't lock the elbow, keep your joints limber. When you can do that with great ease for one minute, put a penny in your hand and do the same thing. Keep the arm relaxed, keep the elbow and shoulder relaxed, don't lock your joints.

What normally happens with drummers (not just bodhran players) when they need to play an extended fast pattern - with a BUNCH of notes/strokes/whatever in a fairly small measure of music, is they get a LITTLE tense, which results in extra tension throughout the length of the arm, into the shoulder and across the upper back. This combines to give you restricted blood flow and all sorts of not good things while you are playing.

The same thing can happen when you are playing something at a more moderate tempo, but find it hard for you to play or to play it for an extended period. RELAX physically and mentally. This will do wonders for your playing.

Finally - relax your grip. If you think is it relaxed, relax it some more. Also, look around and experiment with different tippers. Try a lighter tipper, or a slightly heavier one, then don't try and beat the bejaysus out of the drum. Let the stick do the work (I'm essentially lazy).

The suggestions for fruit juices are good - I tend to drink alot of water, a cups of coffee per set and have a beer next to me. Depending on how long the gig is these will tend to vary a little - 2 set gig, one beer will be plenty. Three sets - I'll start a second beer between set 2 & 3 and have half a beer for after tear-down.

Anyway - I've rambled and am supposed to be at work -

Pete