The ProRing, much like the ribbon, is a must-have piece of armor. It counts as your gauntlet, but it's very much worth the loss of one armor slot. ProRings block RUB and XXXX attacks. Many enemies in the final portion of the game will use these insta-kill spells, and the ProRing is your only protection. On sale in Gaia, these are a must-have for any adventurer.
Buy four ProRings, and mozy on over to the Ice Cave. Go to where the Eye is guarding the Floater Stone. If you walk back and forth where the eye appears, you can fight it an infinite amount of times. Because the Eye's main attack is RUB, and you happen to have ProRings, you'll be immune to his most devastating attack. Each eye is worth 3225 EXP and 3225 G, so getting rich quick is no problem.
One thing I hated about Final Fantasy was fighting those darn Ogres outside of Elfland for G and EXP. A nice alternative, though, are the Kyzoku. All you have to do is hop aboard a ship and hope they show up during random encounters. They're not worth a whole lot of EXP, but they're worth a good 120G each. And when they come in groups of 4, even 5, that's 600+ G per battle. They aren't very tough, either. Unfortunately, they aren't as common as Ogres.
In the Northwest Castle, you'll find some seriously nasty enemies guarding the treasure chests. In particular, the Images that guard treasure chests. These undead are worth a whopping 231G. Each. They often appear in groups of 4 or 5, too. If you've got a White Mage with FIR2, HRM2, FIR3, or HRM3, you'll be fine. Of course, you've gotta have the Mystic Key to get here.
Towards the end of the game, you'll get some cool items with healing properties. Namely, the Heal Staff and Heal Helmet. These items restore HP to all of your characters in battle. It doesn't cost anything, and they don't run out of charges. If you give your characters one of these each, Tonics will be a thing of the past.
The Airship, as described in the Travel section, can only land in grassy plains and fields. Unfortunately, the Castle of Ordeals is plant-repellant and has no fields to land in around it. That means taking a walk, no matter what. To make it worse, there are some pretty strong enemies back there. To avoid the dangerous desert enemies, take the ship and dock it at the river just north of the Castle, then walk a short distance to the south. The Ship might be a slower medium of travel, but it's much safer.
Another great place to make EXP and G easy and fast is in the waterfall. Just inside the Robot's room, you'll find a group of Perilisks, Coctrices, and Mummies. As long as each of your characters has a ProRing, the Perilisks can't do much to you. If you get a shot of FiR2 or 3 off fast enough, the Coctrices will be dead before they even think about petrifying you.
While aboard the Ship, press A and B simultaneously about 50 times in a row. The screen will flicker, and then turn black. A little sliding number puzzle will appear. Get all of the numbers in the right order to win. You'll be rewarded a handsome 100G for winning.
There are some seriously out of place monsters north of Pravoka. In what seems like an error in programming, some random monsters from the northern continent were placed smack dab on the northern tip of the southern continent. Whoops. The fact that it appears in the Wonderswan version shows us that it was either purposefully included in the game, or that Nintendo liked the idea. This is a great place to gain levels in the early parts of the game, if you can survive it. The monsters here are far above the level you'd normally be fighting, so be warned.
As mentioned in the Travel section, the Airship can only land on grass. Luckily, there is one square of desert you can land on with the Airship. Right on top of the Caravan.
In Elfland, next to the White Mage shop, there are three tombstones. Two of them are just plain old tombstones, but the middle one is a surprise. It is the tomb of Erdrick, a character from Dragon Warrior. In the Japanese version of Final Fantasy, it says "Here lies Link" instead. Link being the hero of the Zelda series.