Forms to Keep

What forms are important to keep that financial institutions may not? I had the nasty experience of not having original cost basis info for some company stock (multiple acquisitions, financial institution transfers, etc) and I don't want to be caught off guard again not having saved a form I should have.

Relevant Info:

• Traditional IRA (nearly $200k) - composed of actual contributions ($7k/year or whatever it was at the time + 401k rollovers)
• Roth IRA (nearly $280k) - same note as traditional
• 401k ($125k)
• Brokerage - nearly $500k
• Company Stock (some from an acquisition) - about $40k

I think (please correct me)

1. Cost basis for brokerage and company stock, especially the acquisition. I'll need this for taxes when I sell. Right now most likely retirement age for the brokerage.

2. 5498s if I plan to sell the Roth before retirement age

Anything else? I may opt to retire early if my finances are looking like it/I don't mind living lean, so don't want that off the table forms-wise.