Tools for networking. In addition to a masonry bit as long as my forearm I have the following sorts of things for when I play networking as do most electricians I know that also want to be able to say they do network cables.

Cable/LAN tester. Everything else is pretty much so much good news after this. You want one as chasing down a problem only to find it is a dodgy end is not a good time. You can get a fancy one that grades things and plays tones at you and other such things but http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=4143836&CatId=1797 or something like it will do just as well for most purposes.

Second and probably more useful to you than to me most of the time but if you are buying stuff and they are relatively cheap you want a crimp tool and a bunch of ends. I prefer a ratchet crimp myself but see what suits you (you probably already have a basic crimp tool and have at least used several sets of wire strippers- it is more or less the same action).
The standard for network cables right now and for most of what you will do is usually referred to as RJ45 (I am not sure if anything will change for the many gigabits stuff presently in the pipeline as cat6 is pretty good) although I suppose the technical/modern/accurate name is 8P8C but again everybody understands RJ45. I also stick phone lines down them when kitting out offices and get adapters as do most so whether you also want to do RJ12 or RJ11 I am not sure (I do not know telecoms in Canada I am afraid so do check they are the same standards).
To that end
http://www.monoprice.com/products/product.asp?c_id=105&cp_id=10509&cs_id=1050901&p_id=3353&seq=1&format=3#specification
or
http://www.monoprice.com/products/product.asp?c_id=105&cp_id=10509&cs_id=1050901&p_id=3350&seq=1&format=3#specification
and the ends to crimp on
http://www.monoprice.com/products/product.asp?c_id=105&cp_id=10513&cs_id=1051305&p_id=7245&seq=1&format=2
If you want to take a bunch of wall plates (proper fancy one http://www.monoprice.com/products/product.asp?c_id=104&cp_id=10425&cs_id=1042504&p_id=8731&seq=1&format=2 ) do so although they will probably not get used (most of the time you will get them on a job by job basis).

Hammer and tray of cable clips of all sizes.
Cable wrap- the plastic junk they sell on late night TV and cheap shops. Leave a job site and someone's Mrs does not have to look at a charming rat nest of cables and you will often get the call next time (I don't get it myself but I have seen it happen several times now).

Roll of all sorts of coloured electrical tapes. You find yourself staring at a patch panel or something similar and you be thankful for it.

Speaking of patch panels I also suggest you carry a couple of 2m or so cables, some couplers and maybe a long cable (20m or so) in your kit. A lot of the time it is not worth redoing a cable and nobody is going to want to pay to you stand around for 20 minutes (often when their system is down and has been down for an hour or so by this point) crimping things when you can just swap one out in seconds (and if you are doing the businessman thing return at the end of the day when things have settled down and sort it all).

Secondly although it is rarely used some use it so I might point you to power over ethernet. I have seen a few office style phones and PBX systems use it among other things.
Thirdly it is more or less not used any more but read up on crossover cables (most modern cards and/or routers will quite happily do it for you automatically in software if necessary but you never know when you will encounter some legacy piece of junk). It is just two wires swapped anyhow.
Fourthly I will mention many electricians I know spend their days installing security cameras, phone systems, networks and more so a basic appreciation of how things in the networking world work is good to have (if you can set up a router, DCHP and static addresses, port forwarding and some basic wireless you should be good for much of it). If you have some cables and networking is something you have to do on occasion I also suggest a couple of ADSL filters as they burn out often enough.

Apologies for going off topic a bit but it warranted being said.