Would someone be able to kindly recommend a decent machete? Weight is a factor and so is the dreaded budget. Also, how would I find out if I can get gas (jetboil) canisters in Santarem? Done a bit of googling but no luck so far. Thanks guys.
You can get a decent machete for under a tenner. I have several. You really need to think about the sort of vegetation (and maybe other things) that you're going to use it on before you can sensibly choose one. The usual advice is to use what the people in that part of the world use, but the Amazon covers a large part of the world with a bewildering variety of flora so there will no doubt be a range of tools in active use in different areas.
Here's an example supplier, no connection etc..
http://www.machetespecialists.com/seeallmachetes.html
Personally I like the Tramontina machetes. They're cheap, they're relatively light, they're tough, and they do the job. You can sharpen them with a bit of flat rock.
Sorry, can't help you with the gas canisters. It's always a worry with those things which is one reason why I usually use liquid and solid fuels.