Thanks for the question dude :)
The general rule of thumb I hear most people use is for runs over one hour they’ll bring water and/or gels. For runs 8 miles or shorter I typically don’t bring gel and I’ll drink water if there are facilities available. At 9 miles I’ll take one at the half-way mark and generally take one every 4-5 miles depending on the distance and how much I think I can handle. Some days I am an eating machine and every 4 miles per GU is fine. Sometimes I have to do every 6 and really push it down (like during my last marathon, ugh). I tend to only take GU or those gummy clif blocks, and I can put more time between GUs if they’re the “roctane” type. I also tend to eat the clif blocks slower than the packaging suggests. Clif bloks are suggested as 3 bloks for every 45 minutes (I think) like the GUs, but I’ll take 2 instead and let them last longer. The chewing makes the difference.
As for water, in the summer I’ll drink every 3ish miles, but in the winter I’ll go a full 13.1 without a sip. It’s not the best, but the cold dulls thirst and there are often few resources available like public drinking fountains or bathrooms. I think the water/gu if the run is over 6 miles or 1 hour is a good baseline, but trial and error will suss out all the details that vary from person to person, especially intake rates.