Travel resources
On this page, you’ll find links to various sites for booking hotels, hostels, travel and tours. These are my recommendations which I have found useful based on my own experiences. You’ll also find some links to volcano related sites, including details on recent eruptions, safety, and other information.

Accommodation
TripAdvisor is a good resource for booking hotels, hostels, guesthouses and other accommodation. You can easily compare reviews and prices. Plus, you can also book tours, flights and more. If you’re specifically looking for hostels, Hostelworld is a good option. They also have a chat function in the app which makes it easier to meet fellow travellers. In some locations, AirBnB might have some interesting accommodation. Finally, house/pet-sitting can be a cost-effective way of travelling. Have a look at Trusted Housesitters.
Transport
Omio is a useful site to compare and book trains, buses and flights. However, you’ll probably find more bus options on Busbud. For flights specifically, you can also check Skyscanner and Google Flights. FlightConnections is a great resource to check direct flight routes from your nearest airport and see where you can reach without a stopover (more environmentally friendly). For advice on train travel, The Man in Seat 61 has some brilliant tips on train travel in various countries around the world. For ferries, Direct Ferries is a good place to book. 
When it comes to car rental, I normally book through comparison websites like Kayak or Skyscanner. To avoid the extortionate insurance provided by car rental companies, I normally buy excess insurance separately through icarhireinsurance.

Tours
Get Your Guide is a brilliant resource for finding tours and local guides. You can also find tours on Tripadvisor. Volcano Discovery on the other hand offers bespoke volcano tours around the world.
Volcanology
The Smithsonian Institute’s Global Volcanism Program is the most comprehensive database on volcanoes. You’ll find scientific information, photos, maps, as well as recent activity reports and activity bulletins. It’s always worth checking this site before visiting a volcano.