Congrats on the M1A - love mine and my Bushy.
The "Gadget" is mainly a screwdriver and also for the stock screw (drawing a blank on the proper name here) on the wood stocks.
The GI cleaning kit is good to have. Adds weight. You also get the combo tool. I use a bore snake also.
Don't get your mags from Springfield, too much money. CDNN investments has about averge prices for USGI ($50), also have factory 5 and 10 rounders for $20.
I added a vented handguard, to help ventilation. Looks cool also.
Get a nice sling, I have the canvas and a nylon one.
Spare parts (Fulton Armory), springs, pins, etc.
Too bad you didn't buy a few months back when they had the scope deal. Was the selling point for taking the plunge at that time. $99 for 6x scope and mount, very nice.
The next thing I'm adding to mine is the NM rear sight aperature.
Not as many toys as are available for the AR15, but a fine weapon.