45-Degree Fabric #1
 Fabric  CC BY-SA 3.0

Medium gray fabric pattern with 45-degree lines going across.

Source Atle Mo

 More Textures
Background pattern 227 (colour 4) #2311
 Green  CC 0

A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.

Source Firkin

Background pattern 306 (colour 4) #1877
 Colorful  CC 0

Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.

Source Firkin

3px Tile@2X #343
 Dark  CC BY-SA 3.0

Tiny dark square tiles with varied color tones.

Source Gre3g

Prismatic Abstract Background Design #403
 Noise  CC 0

Prismatic Abstract Background Design

Source GDJ

Zig-zag pattern 2 #2417
 Grid  CC 0

A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.

Source Firkin

Abstract Tiled Background Extended 12 #523
 Noise  CC 0

Abstract Tiled Background Extended 12

Source GDJ

Interlocking pattern 3 #2406
 Grid  CC 0

A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.

Source Firkin

Vintage pattern #1959
 Grid  CC 0

Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.

Source Firkin

Subtle Orange Emboss@2X #98
 Light  CC BY-SA 3.0

A hint of orange color, and some crossed and embossed lines.

Source Adam Anlauf

Desert Camo Print #255
 Fabric  CC 0

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

Stucco #294
 Wall  CC BY-SA 3.0

A nice and simple gray stucco material. Great on its own, or as a base for a new pattern.

Source Bartosz Kaszubowski