Just a short post; but this is how I remember the flags in the EIGRP (RTP) header:
I use the mnemonic “I Can Remember EIGRP-flags.” (yes, it’s not perfect. Sue me).
Then you just need to remember that the byte used for the flags are just like binary bits (because they are binary bits). Each one is just the next largest binary number. (i.e. I=1, C=2, R=4, E=8).