I use a trek "Kid trailer" which has served me exceptionally well. Both for exploring with my little boy, and for hunting. It will hold as much as you can pull up a hill while pedaling.
We usually pack in gear stored into 5 gallon buckets with good snap tight lids prior to the hunting season. All the basic stuff with each scouting trip. Then when we hunt we only need to bring in clothes, gun and some food. When we whack a bear, or deer or whatever we use the trailer to take out the skinned and bagged quarters or in my case just the boned out meat. This way the gear stays out of sight and sealed up between hunts.
I ride in an area closed to motor vehicles but wide open for hunters. Last year while riding I saw two bears near the road eating berries only 20 feet away as I passed them. So now I started to carry the 44 revolver incase that option becomes available again. I don't have the trailer with me on the daily ride, but its easy to go back and get it for game recovery. The good part is that most of the trails and closed roads are down hill when going out.
My trailer was difficult to find because I have disk brakes which are very important when going down hill with 50-75 pounds in the trailer behind you......especially while in a drizzle, or with several inches of snow! Those old "rim grabbers" would wear down like a pencil eraser, or grind away the aluminum rims with the grit and sand on them.
I ride the roads I hunt nearly every single day doing that 15-18 mile loop. Rarely with the trailer except during the season or setting up for the season. Because of this my fitness stays intact and I can manage the trail problems as they come up. For example there was a very large tree fallen across the road/trail. The next day I loaded the chain saw in the trailer and cleared that away on the next trip through. You hardly know that trailer is behind you with under 25 pounds in it. At about 35 pounds you will definately feel it and at 50 pounds you will find some significant level of effort on the up hills. Going down or level 50lbs is no problem though. I've had way more then that on a couple of occasions.
Where motor vehicles are allowed this works way better:
150-200 pounds on the back rack makes for some interesting balance issues but after a few moments of feeling it out you can scoot all the way back to camp.