The tile for this is based on a repeating unit close to a design on Pixabay. It can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
This yellow background consists of a pattern of glossy gold buttons arranged in polka dot style on a seamless texture. Here's a pale yellow background pattern. Feel free to use it for your needs!
Source V. Hartikainen
Zero CC tileable ground (#2) cracked, crackled texture, made by me. CC0
Source Sojan Janso
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Honestly, who does not like a little pipe and mustache?
Source Luca Errico
Here's a seamless brown cork board background texture. Feel free to download or reshare if you like.
Source V. Hartikainen
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Nicely executed tiling for an interesting pattern.
Source Ignasi Àvila Padró
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
A nice one indeed, but I have a feeling we have it already? If you spot a copy, let me know on Twitter.
Source Graphiste
Otis Ray Redding was an American soul singer-songwriter, record producer, arranger, and talent scout. So you know.
Source Thomas Myrman
The edges of all the red objects line up either vertically or horizontally, but it doesn't appear so. Made from a square tile that can be got by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
The following orange background pattern resembles a honeycomb.
Source V. Hartikainen
Fix and cc0 to get the tile this is based on.
Source SliverKnight
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Continuing the geometric trend, here is one more.
Source Mike Warner
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Found on the ground in french cafe in kunming, Yunnan, china
Source Rejon
Alternative colour scheme to the original.
Source Firkin
Prismatic Groovy Concentric Background 3
Source GDJ
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.