I'm still breastfeeding my 9 and a half month too, and your question prompted me to do a google search.
I would think this could only be answered on an individual basis. You should probably raise the question with your paed at your next visit. In the meantime, Kellymom as usual gives a good low-down on Vitamin supplements by category;
http://www.kellymom.com/nutrition/vitamins/vitamins.html
The two most common concerns, Vitamin D and Iron deficiencies are very subjective from the information given and as a general rule of thumb, I'd say if you haven't got any vitamin deficiency it's unlikely your baby will. Having said that, I obviously can't give a medical opinion and you're better off getting you and bab tested if it'll give you a peace of mind!
HK's La Leche League should also be invaluable - maybe you could ask LLL_Sarah who frequents this site?
Iron Deficiency;
<i># Healthy, full-term babies have enough iron stores in their bodies to last for at least the first six months. The current research indicates that a baby's iron stores should last between six and twelve months, depending upon the baby.
"The iron in breastmilk is better absorbed than that from other sources. The vitamin C and high lactose levels in breastmilk aid in iron absorption."
"Breastfed babies don't lose iron through their bowels; cow's milk can irritate the intestinal lining (resulting in a tiny amount of bleeding and the loss of iron)." </i>
Vitamin D deficiency; <i>"Factors that put your breastfed baby at risk for vitamin D deficiency (rickets) are:
* Baby has very little exposure to sunlight. For example: if you live in a far northern latitude, if you live in an urban area where tall buildings and pollution block sunlight, if baby is always completely covered and kept out of the sun, if baby is always inside during the day, or if you always apply high-SPF sunscreen.
* Both mother and baby have darker skin and thus require more sun exposure to generate an adequate amount of vitamin D. Again, this is a "not enough sunlight" issue - the darker your skin pigmentation, the greater the amount of sun exposure needed. There is not much information available on how much more sunlight is needed if you have medium or darker toned skin. See the section below regarding amount of sunlight needed.
* Mother is deficient in vitamin D - this is rare in western countries. The amount of vitamin D in breastmilk depends upon mom's vitamin D status. If baby gets enough sunlight, mom's deficiency is unlikely to be a problem for baby. However, if baby is not producing enough vitamin D from sunlight exposure, then breastmilk will need to meet a larger percentage of baby's vitamin D needs. </i>