Well you may want to consider bringing along another long underwear top to change into when you get to your spot. But then again, you know that you would inevitably have that trophy animal run by, as you're changing, and be gone before you could get a shot off.
Here are some tips. Cotton is bad. It soaks up moisture and holds it like a sponge. Avoid it if possible. Some long underwear that are cotton/poly blends are ok.
Polypropylene is basically a synthetic polyester and is good at wicking moisture away from the body.
Wool is also a good choice as it wicks very well too. And don't be mislead in thinking that having wool on is only for keeping warm. There are some brands that make all wool garments that will, in fact, help keep you cool. Also, the newer wool garments, socks included, are not itchy. If it is merino wool, it should be pretty soft. If it's extra virgin merino wool, then it's really really soft. Rag wool is the old style itchy stuff.
In addition to your long underwear top, look into getting some shirts that will work with your under garments. Go to an outdoor store like Cabelas or REI or whatever you have near you and check them out. You can get button up shirts if that's your style or long sleeve t shirts (or regular t shirts for that matter). If paired correctly, you'll sweat will be pulled into the long underwear and then the shirt will pull some more moisture from the underwear.
When looking for long underwear, or t shirts, keep in mind that the ones that look like they have a waffle pattern (similar to the long johns worn in the olden days) will typically dry faster, if they're made of the right fabric. This is because there is more surface area for the moisture to spread to which thins it out to allow it to dry quicker. It'd be like taking a cup of water and soaking it up with a washcloth and then taking another cup of water and using a spray bottle to spray it evenly onto a thin blanket. The blanket will naturally dry faster.
If you buy something with spandex in it, try to avoid getting pieces with more that 10% spandex because you'll begin to cut breathability. I think it will actually begin to loose breathability at about 8%, but who's counting?
Fleece outerwear. The awesome thing about fleece is that it still insulates really well when it is wet. This would be a great choice if you have a hard hike in really cold weather and still anticipate that you'll sweat a lot. You obviously want to avoid hypothermia.
Anyway, I hope this helps. Let me know if you have any specific questions about clothing and layering.