Parallax RFID reader

I am working on this arduino project where the RFID reader checks what items are in the bag. Is it possible to program the RFID so that it both reads whats coming in and whats going out? I have been successful with reading what goes in but I don't know how to program the rfid reader to read whats going out. I will greatly appreciate any help. Thanks.

I can't see how you will do this unless you have two readers, and you look at which reads first. However, as RFID readers don't work well in close proximity it would be difficult.

Cant you program it so that you set the going in as the first value and just alternate the next one as going out and the next one going in and so forth?

If you are talking about a single reader with unique IDs on the tags then you can write a program that reads a tag and if it has not seen that tag number before adds it to a list. If it has seen that tag before it removes it from a list.

This is similar to the alarm and muster control used in buildings for seeing if everyone who has entered is out of the building when a fire alarm goes off.