not a daft idea atall. Having a catheter (or few) in your pocket is normally enough of a reassurance to enable you to go 'naturally'. Its a 100% garunteed means of going.
I have also done 2 workshops, and I got hold of some catheters after the 1st one as I was anxious about a flight to the US and my stag party. Didnt need it on the flight and had to use one whilst clubbing for my stag, with out one I wouldnt have had a very good time!
It took me a while to obtain however, as I had to see the GP, get referred to the urology department at the hospital, then get referred to a nurse to show me how to use them. Got given enough for free, then a year later I saw the GP again to get a prescription. Took a good few months I think. You can however purchase online (not sure where is best mind)
They fold up so you can take as many as you want in your pockets, are pretty quick to use. The 1st use is nerve racking and painfull, but then you get used to the disomfort. Used one last weekend at a car track day (only 2 porter loos). First time in over a year, and no problems atall!
Go for it, you'll probably never need to use them