There are various means of transport to get around the Kvarner region. Unfortunately a car is the most convenient mode of transport. However there are public transport options to enough locations to allow plenty of options. There are no public transport option to Platak except for during weekends in the ski season. .
Where possible I have given details of routes that are accessible by public transport in the route descriptions.
Inter city Buses
Buses are by far the most useful means of public transport throughout both the region and Croatia.
The biggest bus company is Autotrans, which incidentally is based in Rijeka. However there are numerous other companies. The islands are almost exclusively served by Autotrans. There is no one website that covers all bus routes. The best is Bus Croatia (www.buscroatia.com), some but all Autotrans routes are covered so it's best to also check their website (www.autotrans.hr/en-us/home). Most tickets can now be bought online and printed. Otherwise tickets can be bought at bus stations, or on the buses when boarding in a location without a bus station.
Bags put in the storage space under the bus are charged 7 or 8 Kuna a bag.
Buses do not normally carry bicycles The drivers sometimes allow it if you ask them directly but this can not be relied upon. If accepted expect to pay about 20 Kuna per bicycle.
The ferry options from Rijeka are surprisingly limited. The only ferries departing directly from Rijeka are the fast passenger catamarans run only once a day to Cres, Losinj, Rab and Pag. The Jadrolinija catamaran to Rab and Pag does not carry bicycles. The Krilo catamarans to Cres and Losinj do carry bicycles, charging the same fare as an adult passenger for each bike. It is not well known that they carry bikes which at least means you won't have much competition for a place.
The car ferries from Brestova in Istria to Porozina on the north of Cres and from Krk to Merag on Cres and Lopar on Rab run throughout the day all year round. Bus routes that run use these ferry lines include the ferry journey in the ticket price.
Irritatingly the ferries charge more for a bicycle than for a passenger but it's still pretty cheap.
Time timetables can be found here (www.jadrolinija.hr/en/) However the catamaran to Cres and Losinj is run by a different company “Krilo” which means Wing (www.krilo.hr).
The rail network in the region is very limited, with only a few trains a day and mainly at inconvenient times. However a few of the trains do carry bicycles which makes them useful to get to the mountains. Details of which trains carry bicycles can be found here.
The trains is the most reliable way to visit Delnice in winter which has an excellent full size ice rink.