Dinner and drinks are ok as long as they are not excessive and in line with the expected return for the company, say two people discussing business over lunch or dinner, with a maximum of $x / head. Fairly typical companies will have very explicit rules about what is and is not permitted to the point of spelling out exactly how much you are allowed to spend on a business relationship and the reverse: what to do when/if you are offered an invitation to join for dinner and who is to bear the expense.
Vacations are typically forbidden and would immediately be seen as a bribe. This has led to all kinds of things that are practically vacations but officially are business (such as: conferences in sunny resorts, conferences that take three weeks and so on). Other 'entertainment' can come in many different forms and if not disclosed can get both parties in hot water.
On the whole, pay your own way, do not accept anything that might be construed as a bribe afterwards (so no discount on that shiny item from the company you are deciding to do business with, or not), no gifts over a very low dollar value and in case of doubt clear with legal/linemanager/accountant, transparency is key here, just a failure to disclose can turn an otherwise innocent thing into a potential bribe.
It's really not all that hard to keep your nose clean.
