Smoke

[Magpie]

Good stuff in here. I would reconsider the title, something that gives a bit more than what is already in the poem.

Mom worked nightshift at the hospital. - or something similar so that you can cut next line
We were alone at night.

Dad was in the Navy, - does 'Navy' imply 'traveling' perhaps 'away with the navy'
traveling, killing people. - although at first read I liked the contrast between a Mom saving lives in hospital and a Dad killing but I don't see it's relevance in the poem, 

Dinner was packaged on foil trays.
Wienies and beans. Salisbury steak. - good specific details here - I feel like all the above should be the same stanza

One night the cat's food
caught on fire in the oven.

The neighbor ran over to put it out.
She died soon after - lung cancer. - these 4 lines seem like an odd excursion 

I took up smoking as a teen.
Stealing cigs from shops, hiding
them under a neighbor's porch.
We thought we were cool, but
time eroded that assumption. - good 'second stanza' 

We are the sum of our actions,
spread over time. The past is past,
disappearing like smoke rings into thin air. - some of this sounds cliché 

Today was tomorrow yesterday.
Regrets are a waste of time,
wisps of smoke in the night. - I feel like the last two stanzas are what you are trying to say overall. It would be a better poem if you could say what your saying in these two stanzas without saying it, let the poem say it for you.

Like I said, some good stuff here. I feel like it's missing a final stanza or perhaps two about later in life, we got childhood and teen years then a summary. An additional stanza about later life that says what your summary is saying would suit the nature of the poem well.

Cheers for the read