Checking in at Sal Airport for return journey to UK:
If you are with a tour company, they should be able to keep you updated before you either leave your hotel or arrive at the airport.
If you are not with a tour company you can ask the hotel reception staff to check for you, or look on the internet and website for the flight operator, then under 'timetable' or 'arrivals'.
At the airport - You can also check at the Information Desk in the main foyer area at Sal airport as to whether there is a flight delay, as the information boards aren’t always kept up to date.
Once you have checked in and you have enough time, you don’t have to go immediately through Passport Control, you can go back into the foyer area and use the shops or café. There aren't any meals served in the cafe on the other side of Passport Control, just sandwiches or pizza slices and one or two other items but they are a bit more expensive than the restaurant in the outside foyer, so you may want to eat before going through. It could be a long and boring wait if the flight is delayed, as you can't leave the area.
If the flight is going to be delayed, check with Airport Staff as to what the expected time is of arrival. In general circumstances, you must go through the Passport Control a minimum of 1hr before the flight is due to depart, check if this is still the case even if the flight is delayed! However, I am aware that tour operators have kept people at the hotels if they are aware that there is going to be a long delay.
The café in the foyer of the airport has more choice in refreshments and meals, food is reasonable and so are the prices. There is also a small snack bar upstairs which has a few more choices.
If you have children it may be best to get some drinks and snacks or make some sandwiches. There are a number of shops in Santa Maria where you can buy drinks and food items or you can just visit Cazu, its a mini market that most residents use in Santa Maria. All the taxi drivers will know where it is.