Can police do this?

[Lethal Weapon]

The scenario is,
me and my friend were partying, i'm 19 he's 18 after that we walked home still with alcohol in our bags, we were stopped by the police and he asked the basic questions, then he asked us to open our bags, he confiscated my friends bag and also his alcohol, but couldn't do it to me cause i'm of age, this is in Canada.
What's the law behind searching bags, we weren't doing anything illegal, so is there anything we can do for next time?

[Byu]

Obviously the officer had probable cause, which would have allowed him to search the bag, confiscate the alcohol and arrest both of you. Here in my state it is against the law to possess alcohol if you are under 21. And if you are an adult in the presence of a minor found to possess alcohol you will be arrested for contributing whether or not you purchased it for them.

Byu

[lprocter]

In Canada, it is illegal for someone under 19 to have possession of alcohol outside of a dwelling place (ie a home). As well, it is illegal to have open alcohol in a public place, whether that be on a street or in a school (and other places, obviously).
Most likely, the officer knew that the party was going on (hard to not hear a bunch of teenagers.) As well, you probably were under the influence of alcohol. The officer saw this, and had probable cause to think that you may have been under age. As well, just coming from a party, he may have thought you had some controlled substances (drugs) in your bags. While you didn't, your friend did have alcohol, which is illegal for him to possess outside of a home. And yeah, your friend was doing something illegal.
Next time, don't carry alcohol. It's that simple. When an officer sees two teenagers walking along the street half drunk or coming from a party, he's going to stop you. Just don't carry alcohol.