It really depends on the aircraft. Your F-15C as an air superiority fighter would primarily carry missiles; it can carry four AMRAAMs or Sparrows underbelly (the Sparrow's been all but phased out of the arsenal, but was a common loadout in the F-15's heyday) and four Sidewinders on the sides of the wing hardpoints, with either an additional pair of AMRAAMs or Sparrows on the bottom of the hardpoints or two 600-gallon droptanks (useful for extended CAP missions). That's in addition to 650 rounds of Vulcan 20mm.
These missiles are fairly lightweight; each AMRAAM only weighs about 340 lbs (compare to 500, 1000, 2000 or even 5000-lb bombs), to total no more than about 3500 lbs total ordnance weight when loaded for a "scramble interceptor" profile (get in the air quickly, target the enemy and if they close within X miles, fire at will). It's counterproductive for a plane designed to dogfight to be hampered by heavy munitions (when the F-15 was first designed, the aim was a pure air superiority fighter to combat the perceived threat of the MiG-25, and the mantra was "not a pound for air to ground"). Thus, the primary change in mass and balance during a mission is fuel. If the loadout includes droptanks, they'll be consumed first, as they can be jettisoned when empty (or if an aerial threat closes to dogfighting range or a missile is launched) and even if kept for re-use, draining them first increases the aircraft's roll rate faster in preparation for mixing it up.
The F-15E ground strike variant is a similar airframe with a very different mentality; the aircraft is able to lift a whopping 49,000 lbs of combined fuel and ordnance. It was designed to replace the F-111 Aardvark as a light penetration fighter-bomber for long-range precision strikes on hardened targets using large laser-guided bombs (missions that generally call for a "one pass and haul ass" mentality by the crew), but the Strike Eagle has also been used for SEAD, tank-plinking and other missions generally requiring more total "drops" and thus a more gradual change in aircraft weight and balance.
The performance and handling of the aircraft during ingress versus egress is usually totally different. Enroute, a plane full of fuel and ordnance is a slow, lazy-feeling thing that's really hard to maneuver. By the time you make your approach, though, you've burned over half your fuel, and even with the heaviest bombs this thing can take, fuel is still the majority of the aircraft's max take-off weight. When dropping Mk-82s or laser-guided variants, they typically have to be dropped in pairs; the plane just isn't stable with a one-ton imbalance between the wings (I can't think of many aircraft its size that would be). 500-lb Mk-84s and GBU-12s are still typically dropped in pairs, but it's possible to drop one at a time and keep a stable airframe left to right. The fire control computer on most planes with multiple front-to-back hardpoints, including the F-15, will typically release ordnance front to back, bottom to top, reducing the possibility of the ordnance getting tangled up with others on the way off the aircraft or to the ground (it also helps improve accuracy to use the front stores first as airflow over the weapon is cleaner with nothing in front of it). To maintain weight balance front to back, it is possible to configure the FCC to release from the ends toward the center, but it only matters at all for the F-15E's CFT hardpoints which are in three groups from front to back; it's a bigger deal for a heavy bomber like the B-52, which can carry on external hardpoints running practically the entire length of the fuselage.
Either way, once the ordnance is gone, the F-15E feels like a completely different plane, much more like its air-superiority cousin. The CFTs (and the added targeting pods and the Wizzo's seat) make the F-15E inferior in a dogfight to the C-variant, but it stands a lot more of a chance with a similar loadout versus having almost 15,000 pounds of bombs on the rails.