Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
Prismatic Polka Dots 3 No Background
Source GDJ
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Polyskelion Pattern No Background
Source GDJ
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The classic notebook paper with horizontal stripes.
Source Are Sundnes
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Retro Circles Background 8 No Black
Source GDJ
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
A seamless pattern the starting point for which was a 'light rays' rendering in Paint.net.
Source Firkin
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
A seamless background pattern with impressed gray dots.
Source V. Hartikainen