I'm still in the first tutorial area, White Orchard, but I already ran into the weight limit of my inventory several times. From what I read, I should be able to increase the inventory limit by buying some saddlebags.
Are there any saddlebags available in White Orchard, or where is the first opportunity to get them?
See below the other answers where you can buy one in White Orchard. For other options to get saddlebags:
According to the Prima guide you can win them in horse races.
In addition to saving the Northern Realms from the threat of the Wild Hunt, there are additional activities you can try; and two of these pastimes are fistfighting and horse racing. The former allows you to hone your unarmed fighting skills, and should be undertaken after reading up on the Training section dedicated to this activity. The latter enables you to equip Roach with additional saddlebags, saddles, and blinkers that help you store more equipment, increase your horse’s Stamina, and reduce Roach’s panic level. All are well worth attempting; the horse races as soon as possible.
The location of the races:
Gamezone says you can craft them:
This is from Eurogamer
Once you reach the bustling village of Midcopse, take some time to explore. The armourer has an interesting selection of goods, including two cryptic maps, a range of master and common crafting components, some diagrams, magic items and some pretty decent armour. The nearby merchant, meanwhile, can offer up new Gwent Cards, Horse Blinders to reduce your steed's Fear level, a Saddlebag to increase your maximum inventory weight, plus other treats.
Witcher wiki has a Saddlebag section that is a bit sparse as yet as the game only came out today. It will be updated to show all locations. You can view it here
You can buy them, but an upgraded saddlebag is available to find for free in White Orchard
One of the undiscovered locations, located in the middle of the lake next to the nilfgardian camp contains a better saddlebag allowing you to carry 10 more lbs of weight (30) than the starting saddlebags (20).
I found one for sale at the Armorer's in White Orchard. 180 crowns for 30 extra weight. Hope this helps.
In addition to the fantastic answer above, as of today (19/05/15), with the release of the free "horse armour" DLC, you can buy a Temerian Saddlebag, Blinder, and Saddle from the merchant you rescue from a griffon, near Woesong Bridge in White Orchard.
Theres a merchant over by the king of beggars for the Pyres of Novigrad quest that sells a 100lbs increase for about 800g
70kg bag for 320g available from a trader in Oreton, Velen. It's located south of the Baron's keep.
The blacksmith in Kaer Trolde (Skelige Islands) sold me one for +100 max weight. Hope I helped.
There is a +100, the shopkeeper right to the left of the entrance in the "king of the beggers" area, cheers.
The armor smith in heirarch square in Novigrad sold me a 70+ lbs saddlebags
+70 carrying capacity for 320 crowns sold buy the quartermaster at Chrow's Perch
a +70 has the merchant near the eternal fire temple in Novigrad, costs around 450.
