Help for a 169 mile bike ride
Do I need to put myself through easier challenges/trainings before I embark on my planned trip?


That depends. What is the farthest you've cycled in one go before now? 

I suggest you skip your next gym visit and go for a 10 mile cycle. If that works out, take a 20 mile cycle the next time. 


  What food and equipment do I need?


A spare tube, tyre, mini-pump and tyre levers are essential. So is a helmet. Use winter tyres if you're expecting poor weather conditions or a lot of debris on the roads. (Winter tyres are more resistant to damage)

Panniers are quite nice, because carrying your gear on them is easier than a backpack and doesn't give you a sweaty back. A speedometer is also nice, because it gives you an easy way to see how you are doing (even the cheapest will have distance since reset and odometer functions). 

You will also need: 


Water - however much you need so that you can have about 2 litres (half a gallon) per day. If you can refill multiple times a day, this probably means you're fine carrying one litre (~ 1 quart)
Reasonably energy dense foods - Nuts, bananas, etc... 



  I am travelling in between two cities in Mississippi. What should I be wary of? Or what can I expect?


I'm not familiar with the area, so I can't help specifically with that. 

If you're camping and it gets cold overnight, make sure you have something tasty, energy dense, non-perishable and OK to eat cold. When you wake up cold and your gear is cold, you need some food to help you warming up. Nuts are good.