What type of beverage and in what amount is appropriate for a hotel employee to accept from a guest?
The answer to this depends to some degree on the nature of the hotel and the identity of the guest. In general, it is appropriate for hotel employees to accept unopened drinks of modest value from guests. However, there are some exceptions.
Hotels do typically want their employees to be able to accept gifts from guests as a form of a tip or a gratuity. They want to reward employees for giving good service and they want to make guests feel like their shows of appreciation for that service are accepted graciously. Therefore, they will want guests to be able to give beverages as presents to staff.
The basic guideline for this should be that the drinks should be unopened and meant to be consumed elsewhere. It is not generally appropriate for employees to accept something like a shot of whiskey that a guest wants to buy them. However, something like a nice bottle of wine that the employee could consume elsewhere would usually be appropriate.
Hotels should generally discourage employees from taking gifts that are too large and which guests might later regret giving. Very expensive bottles of alcohol might fit this description. However, in cases like that of a high-end hotel, this rule should be relaxed. Guests in such a hotel are likely to be easily able to afford such gifts and staff should be allowed to accept them