Are there any side missions or quests I should prioritize?

So far in RDR, I've been forging ahead with campaign missions. However, recently I stopped at a Gang Hideout and walked away with a new (and quite awesome) Repeater, as well as access to the Fire Bottles.

It strikes me that there may be some side quests with rewards that would make my life easier, but even after browsing the web for the various side quest rewards, I can't determine which are actually worth doing early, or even which are possible to complete before I've finished the main game.

I plan to attempt 100% at this game, so I'm going to do everything eventually, but knowing now what makes the most difference gameplay-wise would be helpful.

Are there any particular side quests that I should prioritize? Which are they, and at what point should I attempt/complete them?

Solution 1:

After some more extensive playing, I've determined there are at least a few things worthy of prioritizing:

• If you have the GOTY edition (or are willing to pay a dollar), work on unlocking the Deadly Assassin Outfit ASAP. This outfit makes your deadeye regenerate twice as fast, and access to more deadeye meter is always a good thing. Your default outfit confers no benefits, so replacing it is a no-brainer. None of the pieces of this outfit are terribly challenging, and this is all doable in Act 1.
• As you unlock "gang hideouts" they are worth doing immediately. Each gang hideout will give you a new weapon for completing it, and these are typically far more powerful than you'd be able to buy/find otherwise in the campaign. In particular, completing Nosalida early in Act 2 gives you access to both Fire Bottles and the Henry Repeater. The Henry Repeater is one of the better repeater/rifle class weapons in the game, and having it at the start of Act 2 makes several of these missions easier.
• The various single player challenges are worthy of prioritization, as each has a unique and useful unlock at the 10th rank. However, it varies from unlikely to impossible to complete these until you're in Act 3 and have access to the northeastern section of the world map. Still, before you attempt some of the harder things the game has to offer, it's worth it. The 5th rank unlocks aren't nearly as interesting, and most are downright useless. If you complete all 4 of the challenges all the way through rank 10, you unlock the Legend of the West outfit, and double your deadeye meter whether you're wearing this outfit or not. Stacked with the Deadly Assassin outfit's boost, your deadeye meter is nigh unstoppable.

Most of the rest of the unlocks and side missions don't do anything particularly useful except for perhaps some extra money. Money's not in particularly limited supply as you approach the middle of Act 2 onwards, or if you're a dedicated hunter.

Solution 2:

There is nothing to really prioritize in the game. Generally the side quest just rewards you with some amusing dialogue, money, and/or ammo.

The only side mission you cannot do post-game is the stranger mission "I Know You," but that's not needed to get 100% completion.

Take note that you can miss an achievement (Spurred to Victory) for doing 20 missions without changing your horse, if your horse dies or you if hitch your horse at any time before finishing the 20 missions. There is also another one (Heading South on a White Bronco) in single player that involves going to Armadillo on a Hungarian Half-Bred horse.