I recommend you start by having talks with two important people about these proposed outings. First, ask your wife what she wants to do. If she's gung-ho about these ideas, it's time she consults her doctor about the expedition. Your wife's physician knows her medical history and is aware of any special considerations or risks of this pregnancy that might impact her activities. Everyone needs to do this, but especially pregnant women.
Dehydration is thought to be one of the triggers of premature labor.
Eat plenty of healthy snacks . Pregnant women should do this at all times, but they need to up the ante when exercising. She shouldn't carry a heavy pack. Pregnant women shouldn't carry heavy loads, especially as the pregnancy progresses. She should shoulder no more than a lightweight pack with a jacket and perhaps a few snacks.