There are already two answers, but I am afraid that they are skipping a few details that might trip less experienced players.
First, let me re-iterate quickly: your character's wealth is the total worth of everything she owns. This includes the cash she has in her purse, the clothes she wears, the equipment she holds onto, her mount, probably most of what her mount is carrying, maybe a few items that she is loaning to friends, and possibly a shop or house in a distant village.
Second, the game provides wealth guidelines.
When evaluating the "power" of a character, the game assumes that the character has a certain wealth that she has used to equip and arm herself.
If the character has a significantly lower wealth, then she has a handicap and the game will be harder than the published difficulty. Conversely, if she has a significantly higher wealth, then she has a leg up and the game will be easier than the published difficulty.
Not all characters are affected in the same way; the game requires a lot of magic, and therefore characters with less or no native access to magic will suffer more from having access to a lower wealth than recommended (they will not be able to fly, walk on water/breathe water, ...).
Third, just because you have enough cash does not mean you can buy whatever you want.
A small village does not have a hippogriff & unicorn training ground. Sorry.
It's up to the DM to decide on the availability of the items; a rough guideline being that the bigger the town, the more chances that it has expensive/rare items. However you may also wish to account for culture: no Dwarven's Extra Furry Boots in an Elven Town.
Furthermore, just because the crafting guidelines state that a 1st-level spell wand is 750gp doesn't mean that coming across a Ranger's Longstrider Wand is easy. It takes a CL 5 to unlock the Craft Wand feat, which requires a Ranger level 10+ (likely 12) which is rare enough, and one who foregoes the usual combat feat and has picked a craft feat instead. High-demand/low-offer, either the price will rise or the item simply will not be.
Fourth, it is wise to spread your wealth.
Remember the proverb about putting all your eggs in the same basket? What happens when you have to get into a cave/dungeon (pretty rare in this game...) and the hippogriff doesn't fit? Or even if it fits, it doesn't fly? And blocks the way? You have to leave it outside.
In general, the more money you invest into an item, the more dependent on this item you become. If it's unavailable or useless in a particular situation, you are toast.
My personal rule of thumb is to avoid investing more than 25% of my characters' wealth in any single item, and instead of having one +2 swords, I'd rather have one +1 two-handed sword (Slashing) and one +1 silver morningstar (Bludgeoning & Piercing).
I also recommend investing between 10% and 20% of the character's wealth in consumables: potions, wands, scrolls, ... Some items are just cheap (Wand of Lesser Vigor) and others are a "once in a while" kind of items that helps being prepared against a large variety of situations without having to spend precious feats or buy specialized equipment (partially charged Wand of Waterbreathing).