I don't like dry sandwiches, you can easily get a fat reduced mayo or put fat reduced Philadelphia on, it's nice and creamy without the junk fat of mayo, and I would always add mustard for flavor, it's works fabulous, gradually replacing the processed fake mayo. It's not the fat we miss but the flavor, so one can easily trick the taste buds while using healthier alternatives - add mustard to sandwiches, tiny bit of roasted pine nuts and tangy vinegar or tangerins to light salads, shred parmazan on pasta and salads, add curry spice to stews, cumin to veggies, etc. So, basically, spice up when you cut down on the heavy foods.
If you calorie count and do not know the rough value by heart, you will know it after a few days of logging it, then it is smooth. A lot of it is common sense.
Beware, though, of not excluding fats and oils completely, if will make you store fats in your body to stock up. I read people turn chubby when they consume either too much or not enough good oils and fats. I would concentrate on lean protein, some moderate amount of carbs to not feel completely deprived, some healthy fats and ton of juicy and yummy fruits and grilled or baked veggies. Stewing veggies in light chicken broth with cardamom, cinnamon, cumin, tiny bit of fennel seeds is great, salt well and serve over couscous, it's quick and light...
Also, if you over-concentrate on calorie counting, it might make you want to eat ton, happens to some peeps. Brush your teeth every single time after you eat, it might want to beat the cravings. Wholewheat bread will not fill you up on it's own, pack it with a hard boiled egg, some lean turkey and olives, tomatoes and lettuce, black pepper, you will feel full for longer, I'd have that for breakfast, not evening or afternoon, since that's a big boy to digest.