Proofread

Because the weather was so sunny yesterday, my hubby and I went out for a picnic at Sandgate. We had sausages, toast, tomato, and onion. It was lovely.

Could also use the word "since" instead of " because."

I think a better way for the meaning to come across would be - The weather was so sunny yesterday, and, my hubby and I went out for a picnic at Sandgate. We had sausages, toast, tomato, and onion. It was lovely.

Anonymoustomato, and onion.

tomatoes, and onions.

It sunny yesterday I and my hubby we went out for picnic at Sandgate

The way I read this, it sounds like you and your husband noticed what a lovely day it was and decided at that moment that you ought to have a picnic. So, I will edit this for you, bit by bit, based on a "short-term condition or action". Follow along as we reconstruct

It was sunny yesterday. My hubby and I went out for a picnic at Sandgate. We had sausages, toast, tomato and onion. It was lovely.

AnonymousIt was sunny yesterday. My hubby and I went out for a picnic at Sandgate. We had sausages, toast, tomato and onion. It was lovely.

I'd say it thus (which is nearly the same as your version):

It was sunny yesterday so my husband and I went out for a picnic at Sandgate. We had sausages, toast, tomatoes, and onions. It was lovely.

CJ

I think it is not because it is used for formal writing

Anonymous I think it is not because it is used for formal writing

What do you mean Anon?
What is used formal writing in your opinion?

It was sunny yesterday, so my husband and I went out for a picnic at Sandgate. We had sausages, toast, tomatoes and onions. It was lovely.
Note: there is no comma before "and onions".