You don't need any tanks, exit bags SCUBA or any other gas equipment.
Just go to your local welding supply shop and pay a few bucks a liter for 6L of Liquid Nitrogen. You might need a cryogenic container for them to fill you up, but you can get a 6L Dewar on eBay for 150 bucks.
Liquid N2 has two advantages over ordinary compressed air N2.
One: Cheap and easy to source. You probably live within 10 miles of one right now at your local welding shop or dry ice cryogenic store. Dirt cheap at $2 a Liter. For Christ sakes it's cheaper than bottled water! You don't have to know anything about welding at all, just go online and print out liquid nitrogen ice cream recipe. It even says it on the fucking recipes to get the liquid nitrogen from a welding supply shop.
Two: LN2 (being cryogenic in liquid state) expands rapidly when exposed to atmosphere at a rate of 1:700 unit liquid to gas expansion ratio, equivalent to 4,700 gallons of N2 gas or enough to displace the entire atmosphere and it can find space such as a car. Being an inert gas, N2 tricks the brain to thinking you're breathing and normal oxygen failing to activate the body's hypercapnic alarm response. You pass out peacefully in a few breaths or two without the sense of suffocation, panic or distress associated with other gases. Because all you need is a small tent, car, closet or other confined space - you don't need any fancy equipment, just pour the LN2 into a styrofoam cooler and as it evaporates it will displace the composite atmospheric air creating an oxygen deficient environment. At 5% 02, instant death and coma results in a few minutes without warning.