Fallout 4

Jet can be made at a Chemistry Station and it only requires 2 fertilizer and 1 plastic to make. Myrna and her robot in Diamond city sell junk and they always have some fertilizer and plastic to sell. A chemistry station can be found in Diamond City at the Mega Surgery Center. I was able to make about 70 Jet just with the junk i was carrying at the time, so it shouldn't take long to acquire the materials needed for 100.

Easiest solution:

If you're a typical Fallout player, you've probably collected every kind of chem you've come across, so hopefully you should have tons of chems to spare for this.

Simply craft the two special chems Bufftats and Psycho Jet over and over again. Bufftats requires just Buffout and Mentats, Psycho Jet requires just Psycho and Jet. I had just about 50 of each chem so it was no problem for me. Takes about a minute or two to get the achievement doing this method depending on how long it takes for you to spam the A button.

If you need to find some chems there are plenty of traders across the game world that sell them. Obvious ones being the one in Diamond City in the market area, Wolfgang at Drumlin Diner if you sided with him, Doc Weathers who wanders the Commonwealth with caravans (can sometimes be found in Bunker Hill). And of course, chems are located ALL over the world in containers. You should be collecting chems already to have enough to do this method.

I discovered a quick and very easy way to do this. I'm unsure if a specific DLC is needed (very likely it's Contraptions Workshop), but there is a crafting item at Chemistry Stations under Traps called Caltrops. Requires 5 steel each. If you just disassemble everything in Sanctuary and neighboring Settlements, you should have enough steel to make 100 Caltrops. That's 500 steel.

Hey guys, I noticed no solution here for this relatively easy to get but slightly time intensive achievement to get.

I am relatively certain you can get this using a bunch of different methods, and will likely get it over normal play through, but the one I will be using is by cooking meat acquired through trading and killing things.

If you need a cooking location one that I used primarily is Starlight Drive In and direction left of it is Drumlin Diner (thank you Grimace 221) -the woman there is a trader as well as having the occasional trashcan Carla who is a traveling merchant (don't forget you can use wait command by sitting in a chair/stool)

With the use of both of these locations and fast traveling it is possible (depending on your caps, (no you don't need to save) Using and buy any 'uncooked' meat she has and roast it on the cooking location already available at Starlight. For example radroach or brahmin meat.

Please note you will run into 2 non critical not all too difficult named raiders at the diner, and some mole rats at the drive in if it's your first time there. But once cleared you shouldn't run into anything other than the occasional couple of raiders at the drive in.

You can get some fair exp and very good food/recovery items (better and faster than stimpacks in some cases) by using this method. But it isn't necessary to save.

*~ extra but not necessary
The magazine found aboard the U.S.S riptide (directly south of the C.I.T. ruins and north of diamond city you can find a magazine which allows you to collect more meat from animal kills. *re edit others have reportedly gotten the issue with this perk in various locations.

http://fallout.wikia.com/wiki/Starlight_Drive_In ♥

Please comment, I will edit if need be. Just hope this helps!

Easiest and fastest way

Plus

-Achievment not unlocking fix-

Chances are you already crafted 100 things and haven't realised it. If you xbox wasn't connected to live when this happened you didn't get the achievment. Double check on stats. If you have already passed 100 crafted things load a previous save where you haven't yet and disable save.

Okay, depending on how far you went back the easiest thing to craft is caulops (I most likely didn't spell that right). They're little steel spike traps that can be crafted at your Chemstation at red rocket. They cost 5 steel and steel is very abondent in fo4. If you run out of steel at red rocket just warp to another settlement and load back up on as much steel as possible. If you disable saving, you won't have to worry about scrapping whatever you need. It's easier using one ingredient over something that requires multiple. Congrats, you got the achievment super easey!

I have to backtrack to old saves here there because of stuff that didn't unlock when it should have. If you have unlocking problems just go back to an old save, disable saving and bullshit that save to get what you're after so you don't mess your main game up.