Far Cry 5

There are six different collectibles in Far Cry 5, Baseball Cards, Records, Bobbleheads, Lighters, Comic Books, and Whiskey Casks.

Baseball Cards: Talk to the man at the Oberlin Picnic Area. It’s located south of the Whitetail Park Ranger Station.
Bobbleheads: Find Dave Fawler, a man beside a cabin south of Widow’s Creek.
Comic Books: Talk to Nadine Abercrombie on a trailer parked in John Seed Region.
Lighters: Go to Redler Residence in John Seed’s territory. Talk to Wendell to begin the quest for lighters.
Vinyl Records: Enter the Wolf’s Den in Jacob Seed’s region. This guy is a quest-giver, so you may have to complete some other quests before you can get this one.
Whiskey Casks: Go down to the Can of Worms Fishing Store, West of Peaches Taxidermy. Talk to the woman standing inside to begin the whiskey cask hunting quest.

After you begin each quest to find the collectible, most times one of the collectibles are nearby but also go to the nearest shop and in the items section all the way at the bottom you can spend $1200 to buy a map for each of the collectibles ($7200 for all 6 maps) that will place their locations on the map with a marker. Go to the markers and collect 1 of each of the collectibles and the achievement will pop

Here is a Visual Guide for those looking for a Video thanks to Maka91:

Locations:

Baseball Cards
1) F.A.N.G. Center Store
2) Northeast of Baron Lumber Mill
3) Northwest of Baron Lumber Mill
4) Cooper Cabin
5) Widow's Creek
6) Lansdowne Airestrip
7) Cedar Lake
8) Western Mountainside (West of Cedar Lake towards edge of the map)
9) South of PIN-KO Radar Station

Bobbleheads
1) Whitetail Park Visitor Center
2) Baron Lumber Mill
3) Island on Cedar Lake (North of Grand View Hotel)
4) Feeney Residence
5) Lansdowne Airstrip
6) 8-Bit Pizza Bar
7) Bradbury Tractor Shed
8) South Park Entrance
9) St. Isidore School
10) Whitetail Park Ranger Station

Comic Books
1) Boshaw Manor (Mars Comic)
2) Boyd Residence (Vietnam Comic)
3) Bradbury Farm (Mars Comic)
4) Camp Cougars (Mars Comic)
5) Chan Residence (Vietnam Comic)
6) Elliot Residence (Zombie Comic)
7) Jefferson Lookout Tower (Zombie Comic)
8) McNeill Residence (Vietnam Comic)
9) O’Hara’s Haunted House (Zombie Comic)
10) Parker Laboratories (Mars Comic)
11) Peaches Taxidermy (Zombie Comic)
12) Vasquez Residence (Vietnam Comic)

Lighters
1) Abercrombie Residence (Crow’s Lighter)
2) Counselor’s Cabin (Kev’s Lighter)
3) Elliot Residence (Stanford’s Lighter)
4) East of Stone Ridge Chalet & Northwest of Widows Creek (Lefty’s Lighter)
5) Filmore Residence (Dom’s Lighter)
6) Harris Residence (Danny’s Lighter)
7) McCleane Residence (Russel’s Lighter)
8) McCoy Cabin (Tim’s Lighter)
9) Miller Residence (Dusty’s Lighter)
10) Rae-Rae’s Pumpkin Farm (Woody’s Lighter)
11) West of Cedar Lake, across the river from Boat Shop on top the mountain (Joe's Lighter)
12) Whitetail Park Visitor Center (Smiley’s Lighter)

Vinyl Records
1) Breakthrough Camp
2) Linero Building Supplies (Northwest of Fort Drubman)
3) Osprey Cabin
4) MCA Mobile Lab (East of Baron Lumber Mill)
5) North Park Entrance
6) Red Tail Cabin
7) South Park Entrance
8) The Grill Streak (West of Baron Lumber Mill)
9) West of Clagget Bay, West of the Bull Trout (Hard), by the Prepper Stash
10) West of Jefferson Lookout Tower, South of the Wolverine hunting spot

Whiskey Casks
1) Directly East of the Clagget Bay marker on the map
2) Northwest of Forest Research Station
3) Directly North of Forest Research Station, past the island towards the center of the lake
4) Under the bridge North of Vasquez Residence
5) By the Bridge West of Can of Worms Fishing Store
6) North of Silver Lake Summer Camp, to the left of the Island where Ragnar the Terrible is
7) North of Silver Lake Campgrounds
8) Directly East of Tanami Residence
9) Directly South of Oberlin Picnic Area
10) Directly East of Oberlin Picic Area
I'm missing a couple because I've already collected them and they are not on the map, best bet is to start the mission and buy the map so you can find them all. You only need 1 for the achievement though

Rat Pack Achievement/Trophy Guide

Note: I earned this on the PS4 version of the game.
In Far Cry 5 there are 6 different collectibles that you can collect. These include the following:
Baseball Cards
Cheeseburger Bobbleheads
Comic Books
Vinyl Crates
Vietnam Lighters
Whiskey Crates.

For this specific achievement/trophy you will only need to collect one of every item, however, I have created video guides on each and every collectible and their locations to make it quick and easy. You can do this straight from the start of the game once you have access to free roam. You can also purchase Maps for $1200 each from the stores after accepting each quest which will help pinpoint the location if you're still having trouble. If you're low on money, check out my guide for the prepper stashes where you'll earn about $30,000 by the end of it.



Baseball Cards
Head north to the Oberlin Picnic Area baseball field in Jacob's Region and you'll find an NPC by the name of George Wilson who will start you on the Grand Slam Questline.


Cheeseburger Bobbleheads
Head east to the South Park Entrancecheckpoint that separates John and Jacobs region and you'll find an NPC by the name Dave Fowler who will start you on the Mint Condition Questline.


Comic Books
Head west of Redler Creak in John's Region to find the Dodd Residence and you'll find an NPC by the name Nadine Abercombie who will start you on the Golden Age Relic's Questline.


Vinyl Crates
You'll meet the NPC Wheaty during the main mission in Jacob's Region when you arrive at the Wolf's Den. Complete a mission for him and he will give you the Turn The Tables Questline.


Vietnam Lighters
To the North-East of Orville Creek you'll find the Redler Residence and an NPC by the name Wendel Redler who will start you on the What They Carried Questline.


Whiskey Barrels
On the South-East side of Silver Lake you'll find the Can of Worms Fishing Store and an NPC by the name Sherri Woodhouse who will start you on the Whiskey River Questline.