One of the issues with the sandwich is that often, and in Las Vegas I would guess always, there are security cameras recording front desk activities with sufficient views and detail to document money and credit card handling. Probably not being reviewed in real time; mostly in case there is an incident that needs to be reviewed, but you never know.
In those cases, the employee needs to be considering what their jeopardy might be. So if you're going to do it, I suggest you be extremely careful, making sure that the sandwich is shielded and can be passed very discreetly.
*****
Beyond that, simply being nice to people who are providing a service is simply good manners. And in an age where poor manners are increasingly in the fore, showing good manners makes an even better impression.
I recall being on an Alaska flight out of Las Vegas in the middle of summer about 20 years ago, and Alaska had to bump a number of passengers off the plane due to heat. (Available lift on an airplane depends on air density, which decreases with temperature and altitude. There are charts for each plane that show maximum allowable live load (passengers, luggage, freight, and fuel) based on temperature and airport elevation. Under extreme conditions, they can't fly a full plane because the weight exceeds the allowable limit.) The unlucky gate agent was taking a lot of abuse from irate passengers as she was making alternate arrangements for bumped passengers, as if the bumps were something under her control. I took a voluntary bump, because I could work it into my schedule and bump voucher was attractive (at that time, it was a round trip ticket anywhere on the Alaska system).
When I made it to the front of the rebooking line I let the gate agent know that I knew she was doing her best with something that wasn't her fault, complimented her on her professionalism and cool in a stressful situation, thanked her for her hard and diligent work as she was rescheduling under stressful circumstances, engaged in a little bit of light-hearted banter, and just tried to make her time with me pleasant.
When we were looking at alternate flights, the next flight had been completely filled in coach by other passengers who had been in line ahead of me, and she had been giving hotel and meal vouchers to people in line ahead of me, and that is what I was expecting. It turned out, she was actually in a senior position and had superpowers in the reservation system. That next flight still had a First Class seat available, so she gave me a wink and comped me into that FC seat.
If you spread good Karma, sometimes good Karma comes back.
Getting back to hotel/resort check-ins, I've found that being nice can score you things without giving money. After establishing rapport, I might ask the front desk about the room I have been assigned, are there things I should know about the room, and what other accommodations might be available, such as a higher floor, a different side of the building, better access to parking, etc. So I've received quasi-upgrades that way.
My best tale on that front happened at Lawai Beach Resort on Kauai, nearly 20 years ago, when we were arriving on an RCI exchagne. Those who are familiar with the resort will appreciate this.
We arrived relatively early, about 4 pm, so not many people had yet checked. The front desk clerk and I started chatting, just being friendly. I didn't have any design or intent other than being amicable and nice. But then I though to ask where our room was, which naturally was in the Coral Building where incoming exchangers are placed by defualt. I asked if there were any options to for one of the other buildings, and the clerk swapped our reservation with the reservation for another incoming exchanger who had been assigned a room in the Banyan Building (but who hadn't checked in yet.