There are multiple strategies for different scenarios. The idea is basically to load the calf the week before you get to the show, and then let the supplement do its job. I've seen a lot of people overuse or misuse things, and then never try them again because they didn't get them right one time.
For an overnight or two day show I would do this- Start 5 days before you get to the show. Rep-gel 3 days in a row, put it in their feed. Then rep-gel in the morning, aspirinfre paste or aspirin tablets in a bolus at night for two days. The day before you leave, exercise the calf quite well to make sure all the selenium and other good minerals get pumping around in her system. The day before the show, give the rep-gel and aspirinfre paste morning and night, with plenty of exercise. It seems like a lot, but if your calves just don't travel well, this should help.
Another thing is making sure they get plenty of water. And make sure they get electrolytes too. I've seen a lot of calves not walk well due to lactic acid build up from lack of hydration and exercise at shows, but those are usually the week-long shows like a Jr National or state fair.
Things like Natural Stride, Glide, and Lubrisyn can work great, but they're long term. Not really for actute stiffness at shows.