Can you add checked baggage only for the return flight to or from Batumi, and what counts as carry-on with budget airlines?

If your suitcase turns out to be overweight at check-in and you don't want to pay extra, just tell the staff, take the bag back, repack (e.g. shift some items into your carry-on), and get back in line to check in again.

With Citybus, you can check in a large suitcase as baggage and still bring something extra as carry-on.

Several travelers confirmed that checked baggage can be added just for the return leg: fly to Batumi with carry-on only, then pay for 1 checked suitcase on the way back.

If the airline has a small basic allowance, you can usually buy either a larger cabin bag or checked baggage, either for both directions or for only one flight segment.

Carry-on is often not limited to a backpack: travelers use a small soft bag as long as it fits the sizer. One practical trick is to bring a foldable soft bag on the outbound flight and use it on the return together with added checked baggage.