When I buy a pre-mixed salad bag. I cut the top of the bag with a scissors about 1 inch from the top of the bag all the way across and I use that strip I just cut out to tie and reseal the bag. WORKS GREAT!
This page contains the following solutions.
Just like the saying, "one bad apple spoils a whole bunch", one bad lettuce leaf can quickly ruin an entire container of salad. I find this especially true with the baby greens.