You must consider that luggage weight and measurements might differ between airlines. The airlines also use different reference numbers for checking in on each flight, and these will be found on your flight ticket.
Also, take note of the airport from which you depart. For example, on some occasions, you might leave from Arlanda but return to Skavsta or the other way around.
Info: Stockholm Skavsta Airport is an international airport close to Nyköping and is Stockholm's low fare airline destination. Ryanair, among others, offers air travel to/from Skavsta Airport.
The airport shuttle offer departures between Skavsta Airport and Stockholm City (City terminal) customised to the aeroplanes' departure and arrival times. The bus leaves approximately 20-30 minutes after their planes' actual time of arrival.
Travel times with the airport shuttle
City terminalSkavsta approx 80 minutes
LinköpingSkavsta approx 90 minuter
NorrköpingSkavsta approx 55 min
Read more about the airport shuttle here.