I sent an email to their customer care the other day and this was the response I got. Thought y'all might be able to use it as well.

Dear __________,

I would like to provide you with an answer to your question regarding
the number of Extra Bucks that may be used per purchase.

Our registers are set to allow 1 CVS coupon and 1 manufacturer coupon
per item. However, the staff should be allowing customers to use Extra
Bucks in combination with other CVS coupons since these are coupons you
have "earned." In addition, similarly they should be allowing the use
of "offer at the register" coupons, which would be an open offer of $3
off of $15 or a certain dollar amount off of a specific item. Since our
registers are programmed to only accept 2 coupons (1 CVS, 1
manufacturer) per item if the number of coupons exceed the items
purchased a member of management will need to assist the cashier in
processing the coupons. I apologize in advance for any inconvenience
this may cause.


If you have any other questions please do not hesitate to contact us
either by e-mail or by calling (800) 746-7287. Thank you for taking the
time to contact us. I hope you have a nice day.
Sincerely,
Donna Roy
CVS ExtraCare