When I'm backpacking, I go light, but not overly so. I do pack a few luxuries. Over the years however there is some equipment I learned to leave behind. For example the backpacker size Coleman lantern hasn't made a backpacking trip in at least 15 years. A good headlamp is all the light I need and now I only bring the part of the cook set I will need (I never used all four nested pots).
Canoe camping is a different story. Like you, I probably don't use 2/3 of what I bring. Some of that is stuff I still would bring. Things good to have along in case I need them. Rain gear and tarp (for long rainy days), collapsible bow saw, extra batteries, some of the extra clothing. The Roll a Table doesn't take much room and has proven its value over the years, so that stays unless I know the campsites have tables. I guess I can ditch the folding chair and use my Thermarest backpacking chair.
Where I can really cut things down is in the food and clothing category. When I canoe camp, I pack a cooler and that means fresh meat, eggs, OJ for breakfast and cold beer for the campfire. But in the end I wind up throwing nearly half of the food away, or bringing it home. I tend to way overestimate how much I'm going to eat.
As far as clothing, when canoe camping, I bring a change of clothes for every day, plus long pants and warmer outerwear for the evening if it gets cold. In practice however I usually wear the same clothing all trip and only change the underwear. Almost everything else goes home unworn. Sure my clothes get ripe, but heck, I'm camping. So clothing is definitely something I can cut back on.
One of the keys is coordinating with your partners. When it was just and my ex wife, it was easy. Going with others though you can wind up with a lot of duplication. I shared a campsite in the Adirondacks with a woman I met on a Meetup.com camping group. We planned to take my canoe to the site, but it turned out we had so much stuff between us she had to rent her own canoe and we both paddled fully packed canoes to the site. In the end did we really need two Coleman stoves, 8 canisters of propane, two lanterns, two tarps, two coolers of food, two cook sets and heaven knows two what of stuff neither of us used. Coordination before the trip could have really cut down on what we brought along.