Like most said, I would wait until very late October or November to start all day sits. You don't want to burn yourself out early in the season when movement is usually low. Also, hunting afternoons until late October is key. I believe there was a study in D & DH that showed bucks movement were usually late afternoon all the way up until the beginning of November where their movement switched more to mornings. I usually make a whey protein shake the night before I plan on doing all day sits and drink it driving to my farm. It keeps me full for a long period of time since protein takes longer to digest. Bring something to occupy your time. I usually download a bunch of games on my phone to keep my butt in the stand or bring a book. Don't forget the crapper paper!
Hot + early season=not a real good idea to sit all day unless you just really want to enjoy the outdoors. I would recommend only sitting all day if the situation dictates such. I would not get caught up in the pride factor or the "toughness" thing. It means nothing to sit all day if it does not up your chances of killing a deer. When I sit all day I load up whatever I need to be comfortable. I will bring a backpack full of 60-70 ounces of water, a soda for around 2-3pm when I start getting tired, and all sorts of food. I don't skimp. If I am going to walk in a mile at 0500 and not get out of the woods until 6:30pm, then I am going to have whatever I need to be comfortable and satiated. Make sure you layer your clothes to adjust to the changing weather conditions. I will oftern times start out in colder weather clothes but by mid day be only down to a t-shirt and fleece max.
