Had lots of critter experiences while out in the field but I generally go to the hassle of bringing my camera with me on every outing..
I was out walking an apple orchard for deer on a pest control permit a few years back, It was spring time and was carrying my mossy slug gun, a full hydration bladder, a bunch of other hunting gear and my camera gear. So after walking about half the orchard I decided to take a break so I sat down near a dried up irrigation pond. About two minutes later I heard a weird little yip sound right behind me.. and when I mean right behind me I mean within a foot of my head. Made all the hair on my neck stand right up and probably doubled my heart rate instantly... I turned around real slow and found what made the sound as it was staring me right in the face. I sat just infront of an old grown over drain that was about 18" diameter and apparently was an excellent spot for fox den. Four kits were sitting there, three just poking there heads out of pipe and one that had come right out and was sniffing right behind me.. They played in the grass around me for about half an hour, including hunting some mice in the pushed down grass doing the whole head first dive. One of coolest moments I've had with foxes.. The fox population around me is very low and this was a very rare sight.
Another story up north in the Kawarthas I was duck hunting out of a kayak on some small creeks/rivers and kept seeing something in the water up a head.. Didn't think much of it as it wasn't a duck but since the hunting was slow figured I'd check it out. Paddled over to where I last saw the water being disturbed and nothing was there so figured it was just a fish breaking the surface, maybe a carp that hadn't moved out to deeper water yet. I was just about to start heading further downstream and not 10 feet in front of me a head appeared in the water and was staring straight at me.. Turned out to be a very curious and playful otter. I had never seen one around the kawarthas and have not seen one since. It kept going under and popping up at the same distance for about ten minutes and after a few minutes I figured it was worth the risk of getting the camera out and got a few good shots of the little guy.
Next one is not really hunting, but fishing.. I was fishing with my kids at a small conservation area close to where I live.. Just for panfish off a very old dock that is hot used much. Kept hearing a russle on the shore in the brush and figured I'd go check it out with the camera. Got to the shore and found a young mink trying to make a meal of a young muskrat and not really knowing what to do.. The muskrat took to the water and never saw it again, the Mink on the other hand stuck around for about an hour or so and even came out onto the dock we were fishing on for a few minutes, but mostly it was just messing around on the shore.. At one point it was almost sitting on my foot and too close for my camera to even focus on.. I took probably 50 shots of him that day and saw him at the same spot a few more times during that summer. I haven't seen another one out there for three years now.
Found one shot I took before the muskrat took off...