How much line do you really need?

[mtnbykr2]

The "thriftyness" comes out in us all, I guess, I was doing the same with my gear, when necessary I would put a backing of Dacron or heavy mono then
splice the top of whatever be it braid or otherwise, but as I got through the different lines, once I got liking braid I just sucked it up and spooled the reels with the line I thought would work best. Braid lasts seemingly forever so I opted to fill the spool with the line of choice.
I don't think putting a backing on first wouldn't harm anything unless you backed up 65 lb with 20 lb test, really on most occasions you will not see the bottom few hundred feet of line on your reel, but like it has been said, there will inevitably be that "sleigh ride" of a life time, that you may have wished that you put on quality line all the way down... having had a few sleigh rides never come to color, I was happy I had a full spool...IMHO

[vincentek9]

i usually make sure i have 200yds + on my reel. most of my reels are backed with at least 100yd of spectra. my bigger tuna and offshore reels have about 300yd total on them.

[seriola_killer]

You'd do fine with the Diawa 20 sealines for virtually all your yakkin needs!