Good thing i have this cracker is a correct grammar?

The grammar in "Good thing I have this cracker" is technically correct, but it sounds a bit informal and incomplete.

Here are some ways to improve it, depending on the context:

More formal:

* "It's a good thing I have this cracker."

* "I'm glad I have this cracker."

More informal:

* "Good thing I brought this cracker!"

* "Thank goodness I have this cracker!"

The best option depends on the specific situation and the tone you want to convey.