Eat and drink more than bananas and soda, at least burger, pizza, fried chicken, milk, water, tea, and coffee. Eating restores more health and adds fat, but milk can boost your health like kissing and make some fat, tea reduces poison/infection damage, water is inexpensive (just US$0.10) and coffee make you can't pass out for a day. You can drink tap water for free, but it takes time(like Half-Life's health charger) and sometimes force you to poop.