We always offer untouched catering plates etc. to ground crew use. They can do what ever they wish with it and generally we do have very good catering
When it comes to tipping in general, I strongly believe it has got out of hand in the States (no offence), generally speaking.
I remember the times when about 10 % tip was expected at restaurants.
Then it was 15%. Now they recommend and expect 15-20%, and that is even after they ADD 15% service charge in to the bill in some places...
I have no problem with giving some extra for a good service, but I do not understand why tipping should be understod as a compulsory custom, in restaurants or on the ramp.
If the employer can not pay enough salary to their employees, why they don't transfer the cost of the extra dollar or two into prices or fees?
That I would consider fair game.
Then again, just like someone already stated, there is a major difference between different countries and continents.
Cheers!