The Single Most Important Tool You Have

Pepperspray.

Pepperspray in Deus Ex possesses a trait that I doubt you know of. It can disable security lasers. This means you can pass the many lasers in the game that would otherwise be impossible to bypass without expending some of your precious multitools.

To get the best out of your Pepperspray, spray it at the base of the lowest laser. You can crouch under the other lasers in most, if not all, occasions. Remember to not waste it. Spray cartridges can get scarce, but it's better to use them rather than multitools or risk stacking boxes to jump over the lasers (if you're not save scumming, of course.)

When you're spraying at the base of the laser, click only ONCE. This will use 4 units of the Pepperspray, enough to disable the laser. Make sure to aim accurately.

Note that this will only work for some lasers. There is no way, as far as I'm aware, to tell which lasers will go off when sprayed. However, it works for just about every laser in the early-game, when your supply of lockpicks and multitools is still growing. When using this strategy in the late-game, make sure to have an escape plan ready in case the alarm goes off nonetheless and a turret is activated. Unless you're trying for a complete ghost run, using the Pepperspray on a laser instead of multitools or lockpicks is always an option if you can confidently deal with the consequences of the alarm being activated.

Pepperspray is actually much more useful than gas grenades. You won't take damage from your own spray, and it can be used in a radius to stun multiple enemies. However, if you attempt to hit them with a baton and don't knock them out, they can and will wake up from the stun and shoot you in the face, which is an instant kill on Realistic difficulty. A head shot is much safer way of taking out stunned enemies; however, if you're dead set on going non-lethal, then the prod is also effective.

Fire extinguishers, gas grenades, and anything else that may emit any sort of smoke will disrupt a laser. However, this is very impractical because it's difficult to use these items without harming yourself. Stick to the Pepperspray.

Cigarettes do NOT disable lasers. It's unfortunate, because doing that would make JC look like an absolute chad, but as it is, this is only possible with the Shifter mod.

Now, as you have read this, you've joined the ORDER OF THE PEPPERSPRAY. Blessed be the Pepperspray.