Modern Necessities is a 3rd party supplement for Old-School Essentials that adds rules, classes, equipment and more to run your campaigns in any modern setting, including those that mix the contempary with magic and monsters.
The book includes the following:
13 modern themed classes
Rules for giving modern traits to a small selection of fantasy races
56 modern weapons, from pistols to rocket launchers and hand grenades
Rules for special ammunition and firearm attachments
13 modern pieces of armor
54 modern pieces of equipment, from cellphones to night vision goggles
Vehicle rules, including 19 example vehicles
48 Technomancy spells
16 modern example NPC's to do battle against
Extra rules to add more flavor, such as rules for weapon jamming and armor damage