There is so much good information in this thread that it is probably confusing. One thing that may not be clear is whether you need to convert true to magnetic or magnetic to true, and the truth is that it could be either depending on the situation. But the simplest and most common case where an adjustment would be needed is the following:

1) You have a local topo map or aviation chart, the map's grid is True North (which is most common) and there is an indication of local magnetic deviation in the margin.

2) You use the map to determine your desired direction of travel. This will be relative to True North since that is how the map is gridded.

3) You have a compass with a rotating bezel and degree markers. Set the bezel to read your intended direction of travel in degrees true. Now you are faced with making the adjustment. In this case, add declination West.

Example, you want to travel true north (0 degrees). Local declination is 4 degrees West. Add 0 and 4 to get 4 degrees magnetic for your compass heading. Your compass bezel now reads 4 instead of 0 so you will be travelling 4 degrees magnetic (but still 0 degrees true). Since you are adding west and subtracting east declination, the saying "East is least, West is best" is applicable here. Least means to subtract, best means to add.

One way to verify this with common sense is to look out to the horizon and visualize the magnetic north pole being 4 degrees west of the true North pole. The declination image on the map will also illustrate this. Your compass needle is pointing to the magnetic pole and your direction of travel arrow is pointing to the true North pole and they match your visualization of where they should be.

I think this is the only conversion method you need for basic survival instructions.

The most common reason you would need to convert in the other direction is if you are triangulating your position on a map, by taking sightings on distant landmarks. But that is a more sophisticated procedure requiring a sighting compass, pencil, straight egde and some more knowledge, and is probably beyond the scope of a basic survival kit and basic survival instructions. Presumably, anyone knowledgable enough and equipped to triangulate their position would know how to make the conversion in the proper direction for that application. In this case, the "Correct add East" (CAE) method is used, but I would ignore this and stick with the East/Least method for basic navigation.