Why do fighter jets carry missiles almost all the time, even during airshows?

What you will typically see on Western aircraft is a CATM (Captive Air Training Missile).

The blue on that thing is a dead giveaway. Anything that looks like a gun hanging from an airplane that is blue is not real. Sometimes it will be totally blue, sometimes it will just be a blue stripe around it. The real thing will have yellow and brown stripes.

Most of that missile is just ballast; it has no rocket motor, no warhead, and no target detector. The only thing that is “real” is the magic eyeball section at the front (ie not the blue part). This works exactly as a real missile would, allowing the missile to communicate with the aircraft’s weapons system and lock onto targets in the same way a real weapon would. From the pilot’s point of view, the compromise is exactly the same: same HUD symbology, same growl. Except nothing jumps off the railing in a roar of smoke and fury when you press the button.

CATMs are carried around a lot, as the Sidewinder is often used as a defensive missile, so it will be carried for all sorts of training flights. Airplane pilots are obsessed with training for a “bounce” and will generate unexpected attacks on all types of flights.

What you may also see at airshows are smoke generators that are mounted on the same rails as the missiles and are designed to be aerodynamically identical to them:

This is basically just a missile shaped tank filled with oil or diesel and an electrical element to burn it. Why? Well, who doesn’t love a little smoke during a beating?