I'm only as good as my tools.
In all of my collaging so far, I've cought the lowest possible barrier to entry. Below is a compendium of the materials I've used to get started, and links to where I purchased them. A lot of this ended up algorithm driven; Amazon and Google have as good a grasp on my aesthetic predilections as anyone, and fed me accordingly.
The links below lead out to the Amazon listing for each prefab book. Buyer beware!
The Initial Prefab Kit
The "Time Milestone" kit was styled "vintage aesthetic" on the Amazon listing. It has 40 sheets of "vintage aesthetic" construction paper and 25 sheets of precut "washi" style stickers. The washi stickers have a papery, semi-translucent feel, making them texturally similar to the construction paper and great for layering.
Time Milestone
Planet Exploration
More of the Same Aesthetic
The "Planet Exploration" kit came from the same listing/manufacturer as the Time Milestone kit, but features vintage scientific and natural world imagery. This one really fed my love for sea and space, as well as maintaining thematic consistency with the vintage circus notebook and the initial "vintage" collage kit.
Stealing from The Greats
This "Ephemera" collage kit is all classic art. Rather than pepper my collages with more generic imagery, I can incorporate and draw inspiration from actual, known art by famous artists like Van Gogh and Monet. When I saw Helina Metaferia, an artist featured by the Museum of Modern Art, taking pages from art books and "stealing" pieces of existing art for her collages as well, I felt reassured in my impulse to do the same!
Ephemera
What else?
Even when collaging out of prefabricated kits, I still find myself needing an assortment of other tools. These, however, are multipurpose. Call them crafting tools, or call them junk drawer tools, either way you may already have them lying around.
glue stick
scissors
tweezers