The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
Tile available in Inkscape using shift-alt-i on the selected rectangle
Source Firkin
It looks very nice I think.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin