How long after purchase can deli meats be consumed?

Due to new packaging methods that extend shelf life, unopened pre-packaged deli meats remain good to eat longer than they did in the past. They may be consumed up to the "use by" date. Unopened deli meats generally keep for two weeks.
 
However, once the package is opened, the "use by" date is meaningless;  the meat should be consumed within 3-5 days. This is because anti-oxidative gases that preserve pre-packaged deli meats escape from the packaging once it is opened.  
 
Unopened packaged deli meat can be frozen for one to two months.
 Deli meats purchased from a deli counter should be consumed within 3-5 days.
 
Source(s):
Maple Leaf Foods "Listeria and Deli Meat"
USDA Fact Sheet "Basics For Handling Food Safely"