Carheart or Dickie brand.

If it is warm then cotton denim work jeans, I like them in brown, work well and can handle a lot of wear and abuse. the browns are good and both brands have a nice olive drab. Either are nondescript and common rural clothing and blend well without standing out by trying too hard to blend in like actual camouflage does. If warmth and wet are an issue, the all cotton denims don't dry well, then a cotton/poly blend is the way to go.

Both are widely available and run about $17 a pair. For that price I can afford to buy two, maybe three, pairs for what BDUs cost.