My company is hosting some businessmen from Sri Lanka.  We are going to take them out on a boat cruise and, as we typically do, serve small sandwiches, etc.  Is there any food we SHOULD NOT serve so as not to offend?  Thanks!

The only problem with food would be in consideration of their religion. For example, Muslims don't eat pork. Some Hindus don't eat beef either. To be safe, I would suggest chicken.

If I were you, I would talk to a native person from Sri Lanka and learn about the etiquette concerning eating. There are lots of different traditions, customs, etc. that you should be aware of.
Things like when to start eating, how to eat, placement of people, etc. are quite important to a successful business meal. Of course, they will be very understanding of foreigners who don't know their particular customs, but the more you know about them, the better you will impress them :-)