EGC stands for Electronic Gift Card. It is a promotion that Saks Fifth Avenue has every now and then where you get a gift card for spending different amounts of money on a given day. you do not have to be a Saks card holder to get the EGC. The double points event coming up is one where you have to be a cardholder-- you just get twice the points for your purchases during that time (so if you spend $10, instead of getting the normal 10 points you get $20). I hope this helps- if you run a search you can see the different gift card amounts you get for different levels of spending.
Ok- so I don't want to add to the confusion but the promotion of the $400 giftcard for spending $1000 was a one time deal that Saks did this past spring- it's not an event that is guaranteed to occur again and here's how it worked: if you spent a total $1000 or more in handbags and you purchased at least 2 handbags you got $400 back as a giftcard to spend in the store. This handbag promotion is not part of the normal EGC events that saks holds throughout the year.
The regular EGC events work that if you spend at least $250 total in the store on the event day, you get back a gift card. Ex- at the lowest $250 level you get a $25 giftcard. If you run a search, you will find threads that have the total EGC levels typed out.