If you're in the area, it's a decent way to spend a few hours. The usual craft and food stalls, some gun dog stuff, equestrian stuff, air rifles, clay pigeon shooting (on site) and quite a bit of fishing gear usually. A few bits and bobs for deer stalking and the usual falconry displays. Apparently the Land Rover Defenders will be putting on a show - no doubt supported by the AA or Green Flag!
If you can mix it with a day at Drumlanrig or a couple of days fishing on the Nith or stalking in the area it can make for a good few days. £15 per adult (there are some early bird deals).
I usually go every other year and have a decent day as it's not far down the road from here, more of a local show rather than the big country fairs, but if you get the weather it can be a nice place to catch up with folk. I'll probably be there one of the days, but will just pay on the gate.