I have trouble with this, too. I have left SO many carts of items in Target and Costco because I hit my limit and couldn't continue.

I shop strategically most of the time--either on a day when I can get out of work a little early, and go straight to the store, or first thing in a weekend morning. We are talking 6 am early, or as soon as the store opens. That really helps--not many people are out that early--and then I can go through the day knowing that I've accomplished *something*.