In reply to Blunderbuss:
It varies so much from day to day! At 2 years 8 months you will probably find you can carry him a fair distance with a carrier that suits you. The backpack types tend to be heavy with the added weight of the child, so you are better finding something that mimics a sort of hands-free piggyback!
This does take you into the slightly hippy end of the market these things are also not cheap but hold their value really well when you want to sell on.
Your best bet is probably one of the 'full buckle' types of carriers rather than the full on hippy stuff you have to tie. Examples are:
manduca
http://www.preciouslittleone.com/product-information/28/17097/manduca-baby-...
ergo
http://store.ergobaby.com
boba
http://www.bobafamily.com
connecta
http://www.connectababycarrier.com
Babies in space (my current favourite, bulky so doesn't pack down small but so comfy!)
http://www.babiesinspace.com
For all of these, you will be looking for a toddler size (maybe a pre-school but toddler will probably be fine), and you will be carrying him on your back (they are better on the front until about 6 months old).
It is a great investment, our youngest is just 2 years old, and wants to walk most of the time. Some days he really doesn't want to, though, and being able to put him on my back comfortably is just great. He loves the view and being able to talk to us at our height. If he is tired he will sleep in it too. I also use it to keep him under control on the school run or if we ever go into town or somewhere busy.
Occasionally, I will still carry the oldest (now 4) if she is really tired, it is so much easier than giving a classic 'piggyback!'.
If you want to 'try before you buy', you may have a local 'sling library' where you can go and try them, and hire them out for a couple of weeks to see how you get on with it. I wouldn't say that any are better then any of the others, it is a really personal thing about what feels comfortable for you. If you want to find out your nearest, let me know where you are and I will be able to find it for you!
Sorry for the essay! Hope it helps.