A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
This makes me wanna shoot some pool! Sweet green pool table pattern.
Source Caveman
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo
Adapted from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
The image depicts a seamless pattern of a snow crystal.I referred to a book called ”sekka-zusetsu” or "雪華図説" which means an illustrated explanation about snow crystals.This book was published in 1832 (天保3年) or Edo period.For more about "雪華図説",see here:dl.ndl.go.jp/info:ndljp/pid/2536975
Source Yamachem
Prismatic Geometric Pattern Background No Black
Source GDJ