Step 1: Find a Jerry Can, Tent, or Chainsaw. (From here on in I'll be describing these steps with the Jerry Can in mind, however it works the same with the Tent and Chainsaw as well.)

Step 2: Make sure that the Jerry Can is on the ground, and that when you scroll while looking at the item it has the option to put the Jerry Can in your hands.

Step 3: Scroll while looking at the Jerry Can, and select the option to put item in your hands.

Step 4: Now that the item is in your hands, open your inventory, and push the red 'X' on the top-right of the hands window to drop the item once more.
It usually helps to walk backwards in-game while you have your inventory to make this step easier, but as far as I know, it works fine either way.

Step 5: Scroll while looking at the Jerry Can once more, if you've done the glitch successfully, then the option to pick up the item with your hands should have disappeared.

Step 6: Begin walking away from the Jerry Can; if you continue watching the Jerry Can as you walk away, you should notice it eventually disappear. (The Jerry Can will almost always disappear in the first ten seconds after you've begun walking away.)

Step 7: Open your inventory once more, and look in the top-right corner of your inventory where it usually displays your clothing items in little boxes. You should notice that one of these small boxes contains a Jerry Can just like if you had picked it up with your hands normally. However, if you look closer, there is no white hand over the Jerry Can to indicate that the item is being held in your hands; it also doesn't appear in the window at the bottom of the screen, which proves the item isn't in your hands.

Step 8: You should now be able to walk around and do everything you would normally do if you were playing DayZ while "carrying" the Jerry Can in your inventory.

As far as I know, there are only two ways to have the Jerry Can leave your inventory again.

First Method: If you put any item into your hands slot and then take it out again, the Jerry Can should appear onto the ground in front of you.

Second Method: Simply click on the Jerry Can icon in the top-right of your inventory window, then drag it over the vicinity window to the left side of your screen and release your mouse. Doing this will have it appear on the ground in front of you, just like a normal item.

In either of these two cases if you wish to have the Jerry Can appear glitched into your inventory once more, you simply need to execute the "Steps to Reproduce" that I have mentioned above.

I mention this glitch not because it breaks the game in any way, but simply because it gives any player that knows the glitch a rather large advantage over other players. The reason for this being that a normal player would have to carry the Jerry Can in their hands. However, a player who is aware of this glitch can do everything they would normally do without issue, while still being able to carry the Jerry Can with them. If these two players were to turn hostile towards each other inside of the game, the player who knows the glitch would almost certainly win over the one who does not. This is because the player who knows the glitch can instantly pull out their weapon, while the other player would have to drop the Jerry Can onto the ground first, and then be able to pull out a weapon.