If you and your friends expect to possibly get subjected to chemical repression weapons like "tear gas", it may be a good idea to do it yourselves first, alongside with training on countermeasures like liquid Mg(OH)β antacid, lemon juice, milk, coke-type drinks, cigarette smoke, etc.
The primary mechanism intended for their use is to cause such unprepared pain-induced panic that chaotic retreat ensues.
If you live somewhere where possession of such substances is illegal, you can achieve a similar test by frying a large quantity of very strong chili pepper (cayenne or more) at very high heat, as capsicum, the active component of OC spray, the most commonly considered form of "tear gas", is what makes chili pepper taste "hot" and is the mechanism the repression forces use.
Snippet from the GeziDoc (https://vimeo.com/gezidoc 9 hours about Occupy Gezi, in English) when Turkey's rampant dictatorial regime used so much tear gas and similar that it exhausted not just its own store, but also that of Greece and probably elsewhere, to crush dissent for ecology, feminism and democracy.
They even deployed the gas so arbitrarily that they accidentally gassed inside the Consulate of Germany...
