This website is very helpful in your push for 100% in this game. http://www.strengthgamer.com/Red_Dead_Redemption_Guide.html
They have a map of where animal locations are, what is needed to unlock the outfits (and what they do), a guide to mastering the 4 ambient challenges, and an overall map of the locations found in Red Dead Redemption. Hope this helps.
You can track your progress by signing up for Rockstar's site which tells you exactly what you need to do to achieve 100% (what you have completed and what you are missing).http://socialclub.rockstargames.com/
There are 57 missions that need to be completed in the game (though the site only keeps track of up to 48). Currently, the challenges and strangers portions do not work on the site but you can find this information on your stats portion or journal in the game (press start and scroll down to stats or journal. Your completed stranger missions will be on the bottom of the general subsection in your stats).
For the strangers missions, there are 19 in the game but you only have to complete 18. The "I Know You" mission doesn't count because once the game is over, you will no longer be able to do it. For a complete walkthrough of the story missions and stranger quests (locations also), go to this site:http://faqs.ign.com/articles/109/1093822p1.html
Easiest way to complete the locations (which is out of 94) is to simply purchase the location maps at the general stores of every major town that has a general store.
For the mini games, there are 6 of them: Five Finger Fillet, Blackjack, Horseshoes, Arm Wrestling, Poker, and Liar's Dice. To get the badge for it, you must win in all of these events. So that means in Five Finger Fillet and Arm Wrestling, you must defeat every challenger for it to count (Five Finger Fillet is generally 2 or 3 opponents and Arm Wrestling is 1 or 2 opponents).
For the bounties, there are 20 that must be completed: 8 in New Austin (the first portion of the game), 8 in Neuvo Paraiso/Mexico (second portion of the game), and 4 in Blackwater (third portion of the game). It doesn't matter if the bounties are returned dead or alive.
There are five legendary weapons that need to be bought and can be found in Escalera in Mexico and in Blackwater. Those guns are as follows: LaMat Revolver, Mauser Pistol, Evans Repeater, Semiauto Shotgun, and Carcano Rifle.
It is also necessary to complete all 7 gang hideouts. Some will be unlocked AFTER completing some story missions (ex. Tesoro Azul and Fort Mercer). The 7 hideouts are Pike's Basin, Twin Rocks, Tumbleweed, Gaptooth Breach, Tesoro Azul, Nosalida, and Fort Mercer.
There are 9 outfits that need to be completed and to find out the requirements for the outfits, refer to the site provided above. There are more than 9 outfits in the game though so the one's that count towards the 100% are: Elegant Suit, Poncho, Bollard's Twin Outfit, Treasure Hunter Oufit, Bandito Outfit, Mexican Rebel Outfit, Marshall's Outfit, Legend of the West, and Rancher Outfit.
The various properties/save points are also necessary for 100% completion. There are 13 in all and are as follows: Macfarlanes, Armadillo, Thieves Landing, Rathskeller Fork, Irish's Shack, Escalera, Chuparosa, Casa Madrugada, El Matadero, Blackwater, Manzanita Post, Beecher's Hope, and Jack's Bed.
Lastly, there are 5 jobs in the game that need to be completed: 2 Horsebreaking (one in Ridgewood Farm in New Austin and one in Chuparosa in Neuvo Paraiso) and 3 Nightwatch (one in MacFarlane's Ranch, one in Chuparosa, and one in Blackwater).
Hope this helps.