I'm in the ~6mi / 10k crowd here for carrying water. In the summer I drink a lot more if its over 80, but I rarely ran under 6mi anyhow so pretty much always carried water. As for food I havent needed any yet up to 14mi which is about as far as I have gone. I often start getting hungry by 8mi or so, but I just eat a recovery meal when I am done.
I dont really prime anything, I try to not eat solid food within 1-2hrs before. And hydration wise, well if I didnt carry water when I ran I probably wouldnt have any hydration for the whole day sometimes, as coffee in the morning and beer in the evening are probably the only other drinks some days and I don't think they count as hydration.
Edited to add:
Some make it sound like carrying water is a bad thing or a big deal. I know many prefer to not have to cary items, thats fine. For me I have a hydration pack and depending on the run I usually have some other gear with my like backup huaraches, phone, keys, extra batteries if its night time, or gloves and hat if its cold, etc, etc. So 90% of the time I like to have the hydration pack on anyhow just for the easy gear storage. Filling it with a little bit of water is no big deal. Sure in the cold I can probably go 10+ miles without drinking any water but heck even sitting at my office desk for a couple hours I probably ought to drink a cup of water, so why not when I run?