I use a system that a friend who is good at math came up with.
Divide the sale value of the treasure into one part for each character, .5 for the cohorts, and one extra share (or two if you want) as a "party fund." This money is owned by the party and used to get things for the party as a whole (disposable healing items, utility items, ransom, spells for hire). There is an assumption that any standard item can be sold at the wholesale price and any standard item bought at the retail price. Everyones share can be used to buy items out of the DMG, with items that came with the treasure only costing half their sale price, since that would mean they were never sold at half price to be converted to cash to buy something else. If more than one character really wants an item, its possible to buy more and split the financial benefit of already having one in the pot. For instance, say two people want a Ring of Protection +3. It is possible to buy another ring +3 by selling other things, but the person who gets the ring from the pot can buy it for half. So, the fair thing to do would be to buy a second ring and both characters pay 75% of the cost. If three people want it, it would mean buying two more and each paying 83.33% of the cost.