Below are some items from our Amazon Associates offering that aren't the typical Running Store things; except for socks, but these are my personal favorite and may or may not be available locally. You'll likely get your shoes, fueling, etc. from your favorite shop or site, but here's an option for the Odds & Ends at no extra cost to you.
I use this pretty much whenever not running. Sits in the car, on the night table, desk, etc. They say that we're made up mostly of water; and I think they're right.
I'm not going to say that you need to get these. Regular cotton socks aren't ba, but not a terrible idea for "marathon" Race Day and a few training runs.
This may be the best book on preparing for a marathon. The programs go from somewhat to very aggressive. I'm doing the "easiest" one for my next race.
This is very helpful when raining before the Start. Comes in quantity 5 and is disposable yet reusable. A great choice, too, for travel and just to have on hand.
These are the ones for those cold days and/or on the way to the Starting Line (on those cold days). With or without gloves. You might wish you had these.
These actually work. Will be using them more myself; in light of just pulling a tick out of my head. Maybe essential for trail running and definitely for travel.
Consider Fox Labs Pepper Spray when looking for a personal defense item. This is extremely harsh so don't test on yourself and don't ask how I know.
A great do-it-all hydration belt for running. No-bounce silicone grip that contours to the body. Comes with two 8 oz. bottles. Wear low on the hips.
Very light and ergonomic for a relaxed, no-slip natural grip. Expandable zippered pocket on strap for small items/phone. Holds 20 oz. of water.