There is no strictly defined "number" of vapes you can carry, but the TSA and international aviation authorities require that they be for personal use and, most importantly, they must be in your carry-on luggage. Because vapes contain lithium batteries, they are strictly prohibited in checked bags due to fire risks. While you can typically bring several devices (e.g., 2–5) and a reasonable supply of pods or disposables without issue, TSA officers have the discretion to question any quantity that looks like it is for commercial resale. For your e-liquid, the standard 3-1-1 rule applies: each bottle must be 3.4 ounces (100ml) or less, and all bottles must fit into a single quart-sized clear bag. If you have extra large bottles of juice, those must go in your checked luggage. Always ensure your devices are turned off and protected from accidental activation, as many airlines will treat a device that "auto-fires" in the cabin as a serious safety incident.