One thing that is handy is a manual for the engine and outdrive. There are complete service manuals available online at
http://boatinfo.no/lib/library.html.
You can also find briefer, owner-manual-like booklets - at least from Mercruiser, I don't know about Volvo - that address your specific motor and outdrive (you need a serial number from the engine to order these). The shorter booklets contain a much smaller subset of the information from the full service manuals. I bought one of these booklets when I first got my used boat (which didn't have a manual either) and I found it useful. It has info like fluid specs, maintenance intervals, yearly maintenance procedures, etc., in a hand reference that fits in the glove box. Although I generally use the full service manual now, the booklets are sometimes handy if I need to quickly look up something (e.g., what type of fluid to use in the trim pump). If you have a Merc powerplant and you want to order one of the booklets, let me know. I'd have to dig a bit, but I bet I could find the link.
Easiest of all, though, is to ask the question here. You'll get lots of responses, generally, and often very quickly.
Welcome to iboats!
