For my routine, monthly bills such as phone, cable, electric, bank statements, and credit cards, I keep one full calendar year plus the year in progress. This limits me to 2 years at which time I get rid of the previous complete calendar year. Same for mutual fund transaction statements. I save any special correspondence, especially anything related to disputes of bills.
I keep all my tax returns and mutual fund statements. When I was working, I kept all my quarterly 401(k) statements until I realized I could get rid of all of those from the previous plan administrators except for the last one before a switch was made. I kept all the relevant info from the statements in a spreadsheet so the data was never lost. For mutual fund statements, once I get the annual statement I can get rid of the quarterly ones, of course.
I keep all the medical bills and home/health/auto insurance reimbursement statements as well as the auto insurance premium notices for the current car I own. I don't have a mortgage any more and I don't recall what I kept there other than tax-related info.
I have all my canceled checks and old checkbook registers, too.
Retired in late 2008 at age 45. Cashed in company stock, bought a lot of shares in a big bond fund and am living nicely off its dividends. IRA, SS, and a pension await me at age 60 and later. No kids, no debts.
"I want my money working for me instead of me working for my money!"