I like Mike C!'s PPPD system a lot, as it really simplifies the careful calorie-counting I was doing before.
3000 cal. in 1.5# isn't too hard, in my experience. That's 125 cal/oz average-less than the calorie density of ramen cup noodles or Snickers bars (not that you'd want to just eat those). I like jerky, summer sausage, dried fruit and gummi bears, but these are lower calorie density (80-100 cal/oz) so I balance that with some higher density foods like potato or corn chips (150 cal/oz), asiago cheese (130 cal/oz), nut and seeds (peanuts, cashews, pecans, hulled sunflower and pumpkin seeds), etc. Dark chocolate is great (about 180 cal/oz for 85% cocoa varieties), if you have a taste for it. I'm not a fan of most Clif bars--calorie density is relatively low, and the not-so-sweet flavors I prefer off the trail taste like cardboard after a day or two of hard hiking. For me, Larabars work better (esp. Cherry Pie).
For meals, I usually think of dry carbs (100 cal/oz) as the base, and then add higher calorie density ingredients to get to ~125 cal/oz. A breakfast example would be: to regular rolled oats, I add plenty of pecans and toasted coconut, plus sugar to taste and a pinch of salt (I'm sure butter powder would be great too, and I need to look for that). Then boiling water and cozy for a few minutes--much better than packaged instant.