What is the difference between the mass of stuff for a typical human between what they eat and drink, and what they pee and poo?
Well, to a good approximation, it would equal the mass of the carbon exhaled (in the form of carbon dixoide) and the water lost to perspiration and exhalation. But I suspect that doesn’t help you much.
And the mass of what they retain in their body as fat or other new mass?
This bears emphasizing. The primary excretory organ in mammals is not the kidneys, nor the colon, but the lungs.
Depends on whether you are talking short-term or long-term.
If you don’t gain weight over the long term, then the difference is zero. But normal calorie burning is responsible for that.
In the short-term, you gain a small amount of weight that is reduced from the moment you start eating by calorie burning even sitting and eating because the body is always doing so.
I can’t give an exact answer to the OPs question because exactness depends on exactly what food is being eaten and exactly the body’s basal metabolism.
Certainly it’s a very small amount. Say you gain 5 pounds a year. That’s 18000 calories. Divided over three meals a day that’s 16.4 calories a meal. That’s about the calories in a teaspoon of sugar.
What if we just look at the difference before calorie burning is involved? The average person burns 1500-2500 calories a day, depending on the zillion variables of weight, sex, age, and activity. So 500-867 calories per meal go to energy for the function of keeping the body alive. Obviously this will vary tremendously depending on the exact composition of the food at any given meal.
If the OP could come back and clarify what was actually being asked in the OP, that would be a big help.
So, you see, treis, shit doesn’t just happen. It’s complicated. 
I swear that would make a great bumpersticker!
Whatever you got numbers for.
Not true because, as Chronos noted you breathe out a significant amount of mass.
I’m not sure I can clarify my OP any more. You eat/drink X amount of mass, and pee/poo Y amount of mass. The difference X-Y is the mass lost through breathing, sweating, shedding, etc. That difference is what I am looking for.
It is true, because those are the waste products of the chemical processes involved. They’re part of the overal equation.
If you don’t gain weight, the answer is zero. If you lose weight, the answer is negative. If you gain weight, the answer is positive.
There is also a certain amount of mas lost to things like dead skin flaking off, hair cuts and trimming nails.
Again, this is not true because you are breathing out a significant amount of mass.
He’s looking for percentage of mass lost through breathing (plus shedding and trimming your nails) of the overall mass you take in.
Say for every 100 kg eaten/drunk, you pee/poop 30 kg, and the remaining 70 kg is lost through respiration, etc. (made up numbers) I think you can assume the person isn’t gaining or losing weight for the time being. Is that what you are looking for?
The figures I’ve been able to find online imply that a resting person of average size converts about 3-4 percent (by volume) of a given breath into carbon dioxide. Taking the “tidal volume” of the lungs (the volume of an average respiration) to be about 500 ml, and an average breathing rate to be about 15 breaths/minute, we find that [whips out calculator] you lose about 175-225 grams of carbon per day via respiration.
As far as perspiration and water loss via respiration, though, I have no idea. Those are going to be wildly dependent on relative humidity, and not nearly so simple to calculate.