Im a Marine combat engineer and when you get right down to it were not a whole lot different from infantry riflemen, at least in my experience. My load usually consisted of 7 mags (210 rounds), a frag grenade, 3L camelbak, 1L water bottle, 2-3 0.5L water bottles, metal detector (that's where we're different from grunts but some of them sweep too), 4 extra batteries, Kevlar helmet, plate carrier w/ ESAPI plates (30lbs?) and sometimes if I was lucky some C4 (5-20lbs). Machine gunners loads were a lot heavier, 23-27lb loaded weapon (SAW or 240) and several hundred rounds.
For me my load went anywhere from (spitballing here) 70lbs to 90lbs for a 3-5 hour patrol. The longer the patrol the more water I carried and the heavier the load. C4 also tacked on a good bit of weight but I only carried it once or twice a week.
Sgt. of Marines, 3rd Award Expert Rifle, 237/250
1st Award Expert Pistol, 382/400
D Co, 4th CEB, Engineers UP!! OEF 21JUN-20SEP2011