The Bag of Fishing Treasures contains roughly over 7 Gold in cash in addition to rare items such as The 2 Ring, which can sell for a whopping 2,000 Gold on some servers. It can also contain the bind-on-equip Eye of the Sea, which can sell for 400 Gold. Even if you don't have the kind of luck to chance on such rare items, however, it's quite common to pick up insanely expensive gray items such as the Mithril Shaving Razor, which sells for 11 Gold; a Silver Statuette, which sells for 15 Gold; a Beautiful Glass Eye, which goes for 18 Gold; and the mother of all gray items, the Ancient Coin, which goes for a massive 25 Gold.
The white items aren't so bad, either, and are actually collector's items that seem to be aimed at bank toons typically dressed in tuxedo sets. I mean, who wouldn't want a Noble's Monocle? If it doesn't sell on the trade channel or the AH, vendors will take it for a little over 11 Gold. The Ornate Drinking Stein and Antique Silver Cufflinks also sell for 11 Gold while the Gold Wedding Band is a nice 15 Gold item. Some players actually want those items for bank alts or Role-playing marriages. Of course, aside from the nice exclusive gray or white items, there's also a good chance players will get Motes of Water or Elixirs of Water Walking. Even if you won't necessarily want to sell them to vendors, the various baby crocolisk pets are also a nice fishing perk. Although fishing takes a bit of patience (to be honest, it bores the living crud out of me), the Gold that fishing now promises might be enough to encourage some players to take up the skill.