The biggest difference I noticed between training for and being prepared for a full vs a half (other than obviously more mileage) is that knowing how to properly fuel becomes a much bigger deal. What to eat before a long run (13 or more mile training runs) during those long runs and right after is a game changer. I spent a good chunk of time working with a dietitian and also with a running group to dial that in. Went from running a half marathon last October (1:44) to my first full marathon recently (3:53) at the age of 46. Zero issues with hitting the wall at mile 20 (which was my biggest fear) and I ended up with a huge negative split.
I would do a mini carb load the day before which consisted of primarily rice, pasta, veggies, and cutting back on the protein serving size. For breakfast in the morning of the run I’d have a pretty simple breakfast of a bagel, peanut butter and jelly and a banana. I would also drink some electrolyte (I used Skratch). This was also an opportunity to test out different things to see if anything bothered me. That way on race day I had a pretty dialed in what would work for me.