There are usually a few hot snacks....normally cheese or pea pastizzi.

Note that the Hard Rock Cafe was closed for refurbishment last week, but may be open again now. You've got a couple of Costas if you're worried.

In terms of having done Malta, are you sure?
I assume you've done Valletta to death, probably a bit of Sliema, St Julians and Mdina.
Have you visited the 3 cities, Marsaxlokk, Dingli cliffs, the various delights of the north, Gozo (which is where I live).
Then there are the temples, hypogeum, catacombs, roman villa. Did you visit San Anton Gardens, Verdala gardens, Buskett, (I assume you did the Barrakkas).

I suggest you take a stroll at Pretty Bay, which is only about 15 mins from the airport. I'm sure you'll manage to get a coffee somewhere along there.

Or nip into the Corinthia in Attard which does a pleasant afternoon tea which you can then walk off in San Anton Gardens (or around if it is closed). I'd advise you to check first, but I hope you find something more interesting than the LaValette lounge