This may be due to sensitive skin or something....but I CAN NOT wear jeans when I ride for any length of time, unless it's really cold and I'm wearing something under them....which basically means I don't do it. I have tried, and my legs bleed from the chafing. I wish that were an exaggeration. Now if you're not doing anything crazy you probably won't have that much of an issue, but if your skin is prone to chafing, I'd be careful about jeans. Wearing something under them works, or just wearing a different material altogether. Some jeans are made specifically for riding and are stitched in a way to keep the stitches from being between your leg and the saddle, so those may be okay, but I've never dared to try them. Another area to worry about is the top of your boot if you're wearing boots. If the top of your boot has stitching or anything that will rub from movement, wear socks tall enough to protect you.
Have fun, sounds like a great vacation! Riding is really not that painful, but you'll be so much more comfortable if you're prepared!
A horse is the projection of peoples' views about themselves--strong, powerful, beautiful--and it has the capability of giving us escape from our mundane existance.