I actually need to replace mine, it was used to help clean up a from a roll over on Dusey. The ones I use were free from FOTR, an absorbent pad, disposable funnel and a heavy weight plastic bag. If I work on a truck I use an ammo can to drain fluid into and hold oily rags etc. Plastic trash bags on the ground catch drips.
Ammo cans are great for draining lube during field repairs. I usually just use a plastic bag for dirty rags and oily waste myself. it gets burned in the first hot fire we have afterward. Along with any greasy broken birfileds or other mechanical "debris". We fish those out of the ashes in the mornings sans all the grease.
The absorbent pads should be a must have. I usually have a funnel, but I don't really think of it as part of a spill kit.
A shovel for scooping up any oily soaked dirt too of course. NOT for scooping up dirt to hide the oil on the ground.
In some places i would follow this approach as well... Hauling everything out with us. After a visit to the Rubicon trail for example I feel that everyone should have to haul out every bit of s*** that they leave there... their actual feces, not just the trash that they leave...
But.... If I haul my trash out here, it out, it will go to a land fill. No high tech reprocessing. And of course there is the fuel and other resource consumption involved in getting it into the landfill.
If I burn my paper plates and paper packaging, along with a couple/few ounces of petroleum products in an area of several thousand square miles in which maybe 100 people live (None closer than 50 miles to where I might have my campfire) and less than 2 dozen other people travel through on a busy year... the impact is beyond minimal.
Different considerations for different situations.
I ran across one situation that kinda pissed me off a couple of years ago. it was in an are that sees a little more traffic. A spot that we use for family style outings. About 40 miles from the road. Not so much from an environmental aspect, but from a "what a bunch of pigs you are aspect".... Someone had been out on their own family campout.... with kids in diapers apparently.... there was a campfire ring full of used disposable diapers that have been tossed on top of the coals... not burnt of course... and then doused in water along with the coals and left there.
It was simple enough for us to shovel the mess out into a garbage bag... but I was really irritated tht we had to do so. Daydreamed of knowing who had left the mess and dumping it in their backseat for a few minutes, I have to admit.
Fortunately, even at the closer in spots, we don't encounter this kind of lowlife lack of class very often.
I don't know when you were there last but the camping and trail manners on the Rubicon have greatly improved over the past three or four years.
When I started doing the trail our club would typically take out two 55 gal trash bags of stuff, in addition to our own trash. Last time we did the trail we barely filled one bag half way and most of it was our trash.
It seems like most people are bagging their poop too, at least I haven't seen any thing but dog crap on or near the trail for a couple of years.
It has been quite a while since I was there. And I believe it was right before people began to realize just how much impact the biological material was having. I expect it is a lot better now.
I was amazed at the time when I was told that there had been a big clean up just a couple of weeks before I was there. But then I realized that I was not seeing trash everywhere... but (at the time) what I was seeing was a wad of toilet paper and the accompanying leftovers seemingly behind EVERY bush, tree, rock or slightly hidden spot.
It really drove home to me the usage levels of that trail.
When we take people out we insist that they have a garden trowel or small shovel so that they will be willing to carry it with them when they head into the bushes and we expect everyone to bury what they leave. Even though the level of human usage is so low that the impact is meaningless... it is juts as easy to leave no sign at all.
Particularly if it is a spot where we expect to return to pitch camp often over time.
When we have a large group out we often bring along a tent, posthole digger and a toilet seat arrangement to make a camp latrine. A bit of lime to keep the aroma down, and fill the hole when we break camp.
Blue Ribbon Coalition, Friends of the Rubicon, Friends of Fordyce, and many of the local Toyota and Jeep clubs have done an amazing job of education. It has carried over to pretty much all the trails in the Sierra. You rarely see any trash and almost every truck on the trail has a trash bag hanging off the spare.