Far Cry 4
Sidearms can be used while driving vehicles. The best sidearm to have for this is the M79 grenade launcher.
The wingsuit is a very useful tool and you can buy it early on. Check the trading posts.
The harvester perk is useful because it will give you two for each plant and you need two green leafs for a healing syringe. The game will autocraft a syringe if you have two green leafs and space in your syringe belt so this means you can stockpile leaves and keep your syringes topped off.
The collectible maps are a good buy because some signature weapons require you to collect a certain amount.
The Arena is a bit of a grind and you need to get to level ten in order to get one of the better assault rifles. This is much easier to do in the companion app, available on the app store and play store. If you sign in with your uplay account, your rank will sync between the app and game so you can skip the grind by using the much faster app.