Well, spoiled hay which you would not feed to your Cattle Herd!
(Everyone uses sour milk in their coffee right?)
Available at a local garden center, EZ Straw with most of the seed removed!
I several bales of Rice Hulls that I have been using as mulch. High Silica content so good for soil amendment.
My Red Kuri and Bush butternut squash which are starting to "race" around around the garden and I will be getting some EZ straw before they start to really explore. (Killed my first squash nymph yesterday...Got a lure trap that has snagged a number of Transparent Wing moths before they could lay their eggs! Fun!)
We got complaints on that EZ Straw from time to time due to the grass seed that would germinate in it.
I spend a fair amount of time pulling germinated grass out of my beds, but it pulls right out and is a heckofa lot easier than having REAL weeds to pull! :)