Contact customer service - many times by chatting with a customer service representative they will give you extra discounts to complete your purchase.
Keep patient shopping cart - by not completing your purchase quickly, merchants will reach out to you and offer better pricing or more coupons to encourage you to complete the purchase.
Enter multiple coupon codes - combine multiple coupon codes at checkout to score the biggest savings. Also referred to as stackable coupons; combine a sitewide coupon with a free shipping code.
Use reward programs - check out such products as Swagbucks and Shopkick, these companies will give you special discounts and gifts for filling out surveys and shopping around.
Set up discount email - to clean things up, set up an email specifically for collecting coupons and discounts without cluttering your personal email.