YOU SAID:

I should've thought to have brought an umbrella

INTO JAPANESE

私が傘を持って考えている必要があります。

BACK INTO ENGLISH

You must think I have an umbrella.

INTO JAPANESE

傘を持って私を考える必要があります。

BACK INTO ENGLISH

I need to think of me with an umbrella.

INTO JAPANESE

私は私のことを傘で考える必要があります。

BACK INTO ENGLISH

I need to think about me with an umbrella.

INTO JAPANESE

私は傘で私について考える必要があります。

BACK INTO ENGLISH

I need to think about me with an umbrella.