A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Prismatic Geometric Pattern Background No Black
Source GDJ
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Heavily remixed from a drawing in 'Barbara Leybourne; a story of eighty years ago', Sarah Hamer, 1889.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
A seamless web texture with illustration of pale color stains on canvas.
Source V. Hartikainen
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male