I failed to file taxes in 2013 and 2014 -- how do I make sure I'm not forgetting any non-payroll income from those years?

In tax years 2013 and 2014, I became clinically depressed and anxious. Those filings would have included several out-of-the-ordinary (or at least out-of-MY-ordinary) transactions including the sale of stocks and U.S. savings bonds, and the closure of an HSA. I became daunted by the prospect of untangling it all, and handled it in the worst possible way -- I shut down and failed to file entirely. It finally came back to haunt me this year in the form of a garnishment letter to collect the penalties. I contacted the IRS and made arrangements to file those years now.

I have the w-2's and 1099's, but I'm concerned that I might not remember which events happened in which year or that I might accidentally omit something.

Would the bank have filed information about the kinds of transactions listed above with the IRS or do I just track it all down through the documents I do have to the best of my recollection?

Also, are these things I need to submit physical documentation for? That is, if I can find the exact figures of the sales and withdrawals, do I need to submit documents showing them with my filing, or is like the letter my bank sends me telling me how much taxable interest I've earned -- a document for reference that doesn't physically accompany the filing?

I feel so stupid for letting this get away from me and finding it so overwhelming when it probably shouldn't be. Thanks in advance for any advice.