Hi Meggsie,
Glad to hear you will be visiting Killarney. And the Railway Hostel is a good location close to town but on a quiet boraheen (narrow lane).
There are many small restaurants/cafes around the town where you can pick up a reasonably priced yet filling lunch. Jam is my favorite. Evening meals tend to be on the pricey side but there is a supermarket just down the street past the church and you will have cooking facilities at the hostel.
Also, just a bit further down the street is the Arbutus Hotel and Buckley's Bar which will provide free live music but you should probably buy a drink. Mid October will tend to be on the quiet side for pub entertainment and it depends what days of the week you have in Killarney but the town is small and a quick wander around will have you hearing what is available.
As for activities, if you like walking you are in for a treat. Begin walking into town but take the wide street away from the big church on the hill. At the elaborately disguised roundabout take the first exit and follow the wall on your right out of town. There will be gates and a gate lodge where you can enter the National Park. Follow signs for the Knockreer Estate and this will take you through the park to the other side of town by the Cathedral. Follow the river down stream and then left along the lake shore to Ross Castle. You can wander around the castle but it will be closed by October. You can also wander further out onto Ross Island, the Copper Mines and Library Point for a view of Innisfallen Island. Of from the front of the Castle (if you are lucky) you can hire a boat our to Innisfallen Island and stroll around the monastic ruins.
You could hire one of the mentioned Jarvey's from their stand at that elaborate roundabout but be sure to haggle on the price. Unfortunately since you are traveling alone you won't get a good a price as if you were able to share the cost. They can take you anywhere in the two portions of the park but the jaunts to Ross Castle are cheaper than Muckross House.
If you are up to it (price wise people say the are expensive) rent a bike and make your own way to the Muckross portion of the National Park. The bike rental place (which can be arranged by your hostel) will provide a map and send you in the right direction. If you do this, stop at Muckross Abbey and later pick up a togo lunch from the Restaurant by the house. And depending on your energy level, you can ride completely around the Muckross Lake and see Dinis Cottage and the Meeting of the Waters at the Weir Bridge, and onto Torc Waterfall. For a shorter trek from the House though just go along the lake shore to The Old Boathouse and Torc Waterfall. On your way back into town, ride down into The Lake Hotel. Park your bike on the left hand side of the hotel and walk around front, out to the castle ruins situated off the lake shore. Stop in for a drink/coffee at the bar if you need a pick me up!
During the peak season there are many organized tours available from Killarney but by mid October many will have ended. However Deros Tours runs the Ring of Kerry Tour every day of the year and for E27 it is worth it. http://www.derostours.com/ringofkerry.html They maybe running their Highlights of Killarney Tour which is a good way to see the environs if one does not have a car. Pop in and ask the. They are located next to the small church on that elaborated roundabout.
Not sure if I have given you much to go on but please get back to us if you have any other questions or concerns and we will do our best to help.