Yes you can.
You can also use PG (propylene glycol) instead of VG or Glycerin which you may find at feed stores or
buy on the net. Or even mix PG and VG and flavorings.
PG is thinner and will probably work better in a cart than pure VG which is VERY thick.
Glycerine also produces more vapor than PG, but also builds up residue on the atty much faster. You may opt to get both to try as some people have issues with one or the other also.
You can buy USP Glycerin at some local stores/pharmacies, and you could also find non USP grade Glycerin marked as vegetable glycerin in the skin care section. You can find liveley debates as to which is best/safest etc in the diy threads here and having said that I will leave this part alone
On flavorings I can be more specific. You wont want to buy extracts from the spice isle for several reasons: most of them are much more watered down (with alcohol) than what most commonly use to vape with and simply do not produce a good result flavorwise (they are much weaker flavorwise than the other products below) not to mention possibly leaving bad residue on an atty etc.
You MAY be able to find Lorann flavorings locally (craft stores etc) if not you can get them directly from lorann on the web, along with capella's, flavorart, and many other brands. There are threads here that allready have strength meters for a lot of the lorann flavors, as well as discussion as to which are considered better or safer for you and or your atty to use. Most shy away from oil based products and opt for water based ones for safety reasons.
Here are some suggested threads for this topic:
http://www.e-cigarette-forum.com/fo...ehensive-list-flavor-companies-offerings.html
http://www.e-cigarette-forum.com/forum/diy-e-liquid/39795-what-best-diy-liquid-threads.html
Hope this is helpfull.