I've forgotten coin on numerous occasions (a couple of years ago, I went a month without doing a toss of a coin!).
I've twice forgotten a whistle.
Both last season. Once was FL u18 game and, along with the AR's, made way to FOP when I realised. Told them to do pre-match without me and I legged it back to change room!
The other time was my biggest Supply game in my 1st season as a 4. 3rd v 4th, local derby! Lining up in tunnel ready to go out (waiting for last couple of guys) and I went 's**t' and quickly went back to dressing room. Came back out with my whistle in my hand and we all had a good laugh! Got rid of any possible tension!
Never forgotten cards yet, but for those who saw my post in thread about what you take onto FOP, you'll know why! (3 sets of cards!)