I can see not becoming an ultra-light backpacker, but it pays to become a light weight backpacker. This is more about what is left home than the weight of the gear you take. This is one of the nuggets of wisdom a person on this forum gave me.
If your son may someday go to Philmont, chances are he will need a pack sized for him. That's an excuse to get another pack later. I read you can rent a pack at Philmont for $18, so if they have a reasonable selection, that is an avenue to save money. It pays to give the kids a big pack so you can keep up with them.
To give you an example of how well leaving things home can work, I cut my pack weight from 43 pounds to about 26 -28 pounds for a 5 day trip. I carry a three person tent for two of us, so that adds an extra 3 pounds or so. I use an external frame pack and inexpensive gear. The only thing that is ultra-light is my plastic spork.
Little things can have a big impact. For instance, for a camp towel, I use a 6 x 6 inch square of yellow camp towel. I carry one for me and one for dishes. Don't bring a whole roll of toilet paper if half or a quarter roll will be enough.
Your extra pair of socks can be a lightweight sock liner for wear around the camp while you wash your others. Be sure to test drying time on your hiking socks. Many socks will "hike dry," so it's not a big deal if they get wet. (SmartWool stays wet indefinitely. Thorlo socks hike dry pretty well.)
There is no reason for a pot bigger than 2 cups with an aluminum foil pot lid. You can use the aluminum foil from the sandwich you eat a couple hours into the trip.
Plan EVERY meal and snack, and keep each day in a separate 1 gallon Ziploc. The goal is to arrive home on empty, or close to it. Even if you run out, you won't starve in a couple days. (People with sugar problems should follow their doctor's advice.) The rule of thumb is 1.5 pounds for every full day, and about 1 pound for half days. I usually have 81 grams of oatmeal for the last day and no snacks if I can make it out by lunch. I leave some food in the car so I have something to eat for lunch.
Repack all freeze dried meals. It saves a surprising amount of bulk and weight.
Use 700 ml plastic bottles (the kind that come with free water) for carrying water. I usually carry 4 bottles, but only fill one or two. The extras are for filling in camp.
Camelbaks are heavy, and if you ever hike in temperatures around 10 degrees, the water freezes in the hose. Many times you won't need to carry more than 700 ml of water, and most of the Camelback will be wasted weight.
One trick to packing the sleeping bag is to put a strong plastic bag in the bottom of the pack and push the sleeping bag into it. This allows the bag to conform to the shape of the pack. It also saves the weight of the compression sack.
In my opinion, you should get a postal scale and a fish scale. Weigh ALL your gear individually, and weigh it together. Include food and whatever water you have to carry. Then go on "gram hunts" and try to eliminate a few grams at a time. You'd be surprised at how quickly they add up to pounds.
Packs tend to be filled with a weight equal to about 0.7 times the number of liters. If you carry a big pack and have room, someone else will try to fill it for you with their extra gear. Using this formula, you should be able to make do with a Osprey Talon 44 for 2 or 3 days. In my opinion, 50 liters is about the biggest you need for the longer trips, unless you are packing winter gear.