Find yourself a bank that has been around for decades and that has had safety deposit boxes for all that time. Develop your time machine by spending yourself deeply into debt, using funds obtained from shady loan sharks and mob bosses. Go back to, oh, 1938 and pick up a few things:

Action Comics #1 (June 1938) Superman’s Debut, CGC 9.0 – Perfect White Pages

Put items in the safety deposit box. Come back to the present.  Sell the cheapest item, convert to gold; go *back* to the 1920’s, use gold to buy some Tommyguns, come back to the present, mow down the loan sharks and mob bosses, go *back* to the 1940’s, drop off Tommyguns at the FBI; come back to the present. Enjoy your expensive old-timey goodies debt free. Live in the knowledge that if the FBI retained the tommyguns, there just might maybe be a chance that a ballistic analysis might show that the loan sharks were gunned down with weapons that have been in the FBI lockup for 75 years.

Important note: don’t let the FBI know you have a time machine.