The other guys have you covered pretty well: Remo Powerstroke 77 or Ludwig Silver Dot on top and an Ambassador-weight (3 mil) Mylar snare side head on bottom.
On top, the Powerstroke 77 would be my recommendation. The two-ply construction and underlay reduce overtones, drying the drum's sound like DRUMS11 described, and making the drum easier to tune for a good up-close sound. The single-ply Silver Dot tends to be a bit ringy, especially up close. That ring generally blends OK in the context of a whole drum line at a distance (how marching drums are usually heard), but at least to my ears, it's not so pleasing for a single drum up close.
On bottom, I'm one of those Ludwig fans the other guys warned you about. An Evans MS3 or Remo Ambassador will do you just fine, but the Ludwig C1114 seems a little more durable and resistant to stretching, while still giving excellent snare response.
A side note about Mylar snare side heads: Marching and "standard" Mylar snare side heads are generally the same, except for the collar height. The lower collar on the marching head just gives the head more room to stretch under high tension so the rim doesn't get cranked past the bearing edge or bottom out on your lug casings.
Remo and Evans heads are widely available, so you shouldn't have any problems finding them locally or online. Ludwig heads can be a bit tougher to locate, though. If you want to give them a try, you can order through
Cascio Interstate Music.
Oh, and since you're a drum set player... Speaking of Ludwig heads, their coated medium heads are great on snare drums or as single-ply tom batters. Nice warm sound and the coating's really durable. I generally like them better than Remo Coated Ambassadors or Evans G1's.
Have fun with your new (old) drum!
...and have you picked up a pair of marching sticks?