This question doesn't have a simple answer, so much depends on what you are shooting.
If I am out doing scenics, or night shots etc. I will have time to think about every shot properly before I take it. I may only take a handful of shots during a day out shooting, but I would expect them all to be "decent" shots, with hopefully one or two I am really proud of.
On the other end of the scale, I might be shooting drag racing. In that sport spectacular incidents can happen without any warning, if you try and react when it starts you have missed it. So, I capture the start of every run using burst mode, resulting in maybe 20 shots or so from each few seconds race.
Virtually all of those will be binned, I would hope after a weekend event (and several thousand shots) to have some decent shots around the paddock, some more taken as cars manouevre around the staging area, and mechanics work on them and I will generally keep the best pan shot of each interesting car as it blasts down the track.
I have never worked out my "success" rate, but most paddock shots are technically decent, plus I have had time to set up properly for each shot, and choose my angles and timing for a decent composition. In the end I will only pick the most interesting ones to work on, the others will be record shots of the event. Again, they should be mostly "decent" shots, with hopefully a few really nice ones.
Start line shots give a little less time to prepare, and angles are compromised from not being able to move around the subject the same. I would again expect most to be technically decent, but again will only work on the ones I really like, this will be a lower percentage of shots than with paddock shots.
Now, the racing shots. These should be correctly exposed etc. but because I am panning, and trying to show the speed with a relatively slow shutter speed, I expect a proportion to be lost to lack of sharpness on the vehicle. In addition this is where most shots get binned because the composition isn't great. A burst of several shots as a car comes off the line and passes me will be mostly uninteresting shots. If it does a good wheelstand, then there should be a nice one at it's highest point, plus I will hopefully get a nice pan shot as it comes by me. The shots going up and down in the wheelstand will be binned, as will the shots as the car approaches my position and goes away from my position, as the angle will not be as good as the one pan shot as it passes. So, probably 90-95% of actual racing shots will be uninteresting and not "decent" shots and be binned in the first cull. I will then select my favourites from what is left to work on further, to hopefully come up with a few good action shots I really like.
At an airshow, I tend to shoot a lot less shots, preferring to time my shots to give a good composition but again, keeper rate can be fairly low. With jets, I have a much higher keeper rate, as I use a faster shutter speed and most shots should turn out pretty decent. Prop aircraft though are shot at slow shutter speeds to get good prop blur. Keeper rate depends on how much I want to push that slow speed, I tend now to go quite slow and accept a high rate of shots will not be sharp enough, but that the I should get at least one decent, sharp shot with a good angle on each plane and pilot, and it should have really nice prop blur. I go for one really good shot, rather than a handful of lesser ones at a faster shutter speed.
With birding shoots, I expect to miss focus with some, don't necessarily pan accurately enough etc. So, again I expect some crap amongst the good stuff.
Keeper "rates" are really variable therefore, depending on what you are shooting, how much time and freedom of movement you have to set up each shot, and how much you are pushing the technical envelope in the cause of more "artistic" shots.
I would rate my percentage of "good" photos per shoot therefore as anything between about 5% and 100%. That percentage does not concern me, so long as I come home with some good shots (and hopefully one or two I really like) and haven't come away with nothing of something I particularly wanted to capture, such as an unusual aircraft at an airshow - I would want at least one shot of it, amongst the good stuff.