First have some snacks of course. .lol.
If you are on Playstation. hold down the select button. Dont tap it. That changes your view. Hold it down. It will pull up a menu. Go to Inventory. From there it will have all of your snacks. Meteorites, P&Q's etc. It will also have cigarettes if u have any. Dont use those. lol. will decrease your health. lol.
If you press on a snack your dude will start eating. It fills it your health up slow. My recommendation. Do this while you are sitting in your car or while you are in cover.
When you are in cover just press on the food item from your inventory. If you are low health you can replenish in like a second. You can eat like 6 snacks real fast. From the inventory menu you can also select body armor. Put on a new armor too.
First thing I do when i hit free roam is hit the gun store. make sure i am fully stocked up on stickie bombs and armors. then i hit a 711 store. i stock up on all snacks. Then rob his ass.