I live in Flagstaff so I have hiked in the canyon a few times overnight; and more so on day hikes.

It is really hot and dry; do not underestimate the need for water (how hot the water will get) and remember that even if there are noted springs on certain trails at places before you get to the river; some of them do not exist during the summer months. Start early in the morning, even hike before it is light if you have good lights and are not on one of the more adventurous trails.

The good thing is when you are buying your pack; and you are planning on hiking in the summer; you do not need to carry as much so you do not need one of the great big bags! I use a bag that is smaller (I will be at home later and will get the dimensions of the bag). You don't need a sleeping bag in summer in the canyon only a sheet or light blanket; if you plan on camping on the rim, you will need more. I usually don't hike in the heat of the summer in the canyon (don't need to since I live so close) but my husband has. He was amazed at how much harder it was and how hot it really felt like. He was quite fit at the time too.

I don't know of any way to really train for the GC either. It is all up and then all down; so there is nowhere else that you can get that much of a sustained up and down to get used to the GC. I usually try to do as many fitness hikes in the mountains that consist of hiking up and down, but even that won't quite keep you from getting sore. There just really is nothing like the GC!

Remember that even if you get a permit to hike in the summer months, there are warnings on the permits that say something like; this hike is not recommended; it is dangerous and you should not do it! These warnings are not to be taken lightly; it is dangerous in the canyon in the summer