Mate, if you move any illicit substances over international borders there is no 'own use' that is called drug trafficking.
I very strongly suggest you do not engage in this behaviour, unless you are willing to risk some extremely serious consequences that you may not be entirely please with.
Own use refers to Australia's specific drug laws which vary state to state where small amounts of each drug have been decriminalised and you'll get a fine, a slap on the wrist and maybe some drug court as a result.
If you go through customs with anything illegal on you which is a drug, you are trafficking narcotics over international borders and that is not just a crime, but a federal crime.
Is bringing the drugs really worth the possible sentence?
I don't actually know what substance cold is, and for future reference please refrain from using slang on the forums as people use different terms all over the world so it can be hard to identify what you're talking about.
If you mean Coke or meth, just don't bring it with you. Be a big boy and wear the comedown as a consequences of your actions.
If it's heroin you're in for a shit time and to be honest a bit of planning for this trip wouldn't have gone awry as you definitely could have reduced your use and planned a withdrawal.
Ketamine again just don't bring it.
MDMA don't bring it.
I'm sorry, but literally none of the consequences from not bringing a small amount of drugs with you which probably won't even last you the duration of your holiday are worse than being charged with a federal level criminal offence and potentially looking at 8-10 years behind bars.
I'm almost an admitted lawyer though, so I guess what the fuck would I know about crimes, punishment, sentencing, and what your life may be like if you do something as senseless as this.
No one on this forum will give you legitimate advice about how to commit a federal crime. We do harm reduction.
If you are deadset on doing this I suggest putting some money aside before you go for the criminal defence lawyer you will inevitably require.