This 0 tick generator functions without nether resource or slime. Easy to build early as soon as redstone and iron is found.
1 Redstone block (aka 9 redstone dust)
7 Redstone dust
2 normal pistons (aka 2 iron, 2 redstone, wood and stone)
1 slab (any material that doesn't interfere with the signal)
5 blocks (any material that doesn't interfere with the signal)
For the building instruction check the attachment.
I looked into 0 tick generators for my bonemeal farm in my 1.14 hardcore game. But im still early on, don't have diamond yet and therefore no access to the nether either. Also don't feel like searching for slimes without proper equipment. I couldn't find any 0 tick generators which i could have build with the resource i have tho, so i came up with my own one.
Not claiming the idea of this one of course, if it exists i just couldn't find it anywhere. So i decided to share for other people to have it easier.