The components I'll be using at the start of this this project are:
The Data logger shield gets plugged onto the Arduino. However, this makes it difficult to connect anything else to the Arduino, certainly in this prototyping phase. So, before soldering together the Data logging shield I ordered some extra connectors from Ebay and cut these up to the appropriate size.
Once the Data logging shield was put together I soldered these connectors onto the Data logging shield. This allows me to use all unoccupied data connections of the arduino e.g. for the parallax RFID shield.
To make sure I'm not trying to use the same pin outs for 2 different things I'm falling back on ShieldList website. The contain all the pin outs for every shield possible.