Q 334 How can Brew Potion be considered a useful feat if one already has Scribe Scroll?
A334:
Firstly, generally it's not considered a good feat. It's limited in what spells can be used, and it's expensive.
However, as mentioned anyone can use one, and there's at least one feat that allows you to drink a potion but delay the effects until later, allow you to prebuff with one potion. Not exactly amazing, but it's something that is possible.
Finally, as also mentioned items (usually bandoleers of some sort) can allow you to more easily access potions on your person. I know of one that's worn on the arm, but I think if you are struck in combat there's a chance one of your potions will be broken. I think it's from a campaign setting, maybe FR. Additionally the PF SRD mentions just a regular belt that allows the same ability, without risk to your potions.
Edit: Q335: To qualify for level 3 spells for prestige classes ASAP do you need Versatile Spellcaster, Sanctum Spell and Heighten Spell or just the first two? Can someone explain? I tried to search the forum using the built in search but almost all the hits are people using it to qualify, and not an explanation.