This is simply not true with regards to recreational vessels to the degree you're positing.
I have extensively researched this matter, and the language is clear in the law involved - and it is black letter law.
I've talked to the USCG personally about this as well, and as I said, it simply isn't an issue. There is NOTHING wrong with splitting fuel and operating expenses - nothing whatsoever. There is also nothing wrong with your friends bringing food and beverages aboard.
There is no way that your expenses in operation of a boat are limited to the fuel you consume. No chance in hades. So long as you do not take an arbitrary amount of money as a condition of carriage, that is, people voluntarily contribute to the actual costs of the voyage (which of course cannot be reasonably determined until you return to the dock), you are well within the safe harbor provisions of the law. This is true even if you go out with three or four friends and at the end of the day they fill your entire tank (e.g. you pay for none of the fuel); you're STILL in the clear, as the operational cost of the vessel over that period of time is in no way represented by fuel burn.
That you run every Saturday isn't an issue either. If you work Monday through Friday, and dive Saturdays, and your boat runs every saturday the weather is reasonable, you're still fine.
In reality what happens if you truly do things on a voluntary basis (that is, you're doing things within the law, not trying to run a "back door" charter service) is that you'll take your best guess on fuel consumed for the day, make it known what that is when you get back to the dock, and everyone gives you whatever they wish.
Your "enforcement" is limited to not inviting someone who gives nothing (or far too little) on the next trip. You're not taking them out for money - they're your FRIENDS. If they don't stick around to wash up the boat and act like friends, you don't take them the next time!
Where you can get in trouble is if you start telling people "I'll take you diving for $50 for the day." That is clearly a "for-hire" operation.
If some commercial outfit tries to make trouble for you, they would find themselves on the wrong end of a really nasty civil action - at least they would if it was me they wanted to play with. I know where the line is and stay WELL on the "right" side of it, and am more than happy to make a LOT of trouble for anyone who tried to cause me problems for their pecuniary benefit.
Insurance is an entirely different matter, but real marine insurance companies have no problem with this sort of thing, as its done literally every day. I've yet to go out on ANYONE'S boat (other than my own of course) and not hand the owner some cash when we get back in for fuel. This is not just a common practice, its "how its done" with privately operated vessels, and no real marine insurance company is going to have a problem with it.
If you don't have real marine insurance (and no, companies like State Farm do NOT count) then you might indeed have something ugly in your policy - check it closely. Then again, check it closely anyway - if you don't have agreed value insurance, environmental coverage and the rest that you get with a real marine insurance carrier, you need to switch to one for completely different reasons.
Civil aviation is an entirely different matter - I've glanced at those rules but have not looked extensively at them, as I don't fly. But friends of mine who do have told me that technically I cannot put fuel in their plane if they take me somewhere without them being technically in violation of the rules regarding their non-commercial private-pilot's license.
That provision IS in the USCG regs and was EXPLICITLY added to cover this situation.