What healthy and natural thing can I take or what can I do to stay prevent falling asleep on a long road trip.?

Ideas. When on a long trip of any sorts, breaking time up can be helpful. You may want to set timers and play games. Thinking like listening to audio book or podcast can help and changing focus (actually changing books after 30 minutes to 1 hour) can be helpful. Chewing gum/eating but don't want to add a ton of extra calories. The last recomm.--> stop and brisk walk for 5 min every ~60 miles.
Know your limits. Your best bet would be to simply know your limits. The effects of artificial agents to keep you awake are unpredictable- you can take some crazy stimulant and still nod off driving if you push it too much. Know your limits. Know when to stop to eat, and when to stop for the day. Be safe.