I haven’t been to LaGuardia recently but in other airports eating and drinking is allowed and you can buy snacks and water/drinks. The expectation is that you remove the mask for short periods while eating & drinking and do so at least 6 feet away from anyone else. Most people I saw did comply with that.
In Newark (EWR) one sit down place was open, the tables were far enough apart so that people could eat without wearing a mask.
Practices in lounges vary greatly: “closed”, “no food or drink”, “only pre-packed snacks or water, but must eat outside”, “some food and drinks for consumption inside but no alcohol”, etc.
Caveat: Details vary with the specific airport & terminal and regulations do change quickly with little or no notice.