In reply to Roadrunner6:
Late to the party for advice here, but I just did my first 100 mile run last weekend. It was a self-set course, rather than part of an event as I was doing it for charity and didn't want it called off due to Covid (and also wanted to pick the best weather window).
Aside from the fueling stuff (salty potatoes and watermelon being my choice), my advice is if you can run most of the course beforehand this is a great advantage so that you don't have to concentrate too hard on nav, and you can judge how you are going. My longest training run was 50 miles, which was the first half of my route - and the bit I was least familiar with. On the day of the 100, I found it extremely encouraging that I was getting to the same spots much fresher and feeling strong. On my 50 I'd hit a wall at 35 miles, but on the 100 I was still clicking along up until about 60. Mentally this was great!
And with the strong chance of sounding boastful, I actually really enjoyed the whole run. People often say "enjoy it" which can be a bit cliche, but if you prep well, you will. I got to the end without a single blister and was still able to smile, and walk/wobble the extra mile back to the carpark. And did it in under 24 hours which was a personal target.
If you want any tips (not claiming to be an expert by any means) that are fresh in my mind, PM me.