Actually at our Tru Green branch one year about 1978, a woman came in and tried to sell the manager on small plastic rain guages with our name and number on them. I think we ordered a couple thousand. (Not sure if the poor lady ever got paid). I don't recall exactly how we used them in our marketing plan. They costs us about 50 cents each. (maybe).
Actually you could enclose a half an ounce of grass seed for weight in your promotional bag. Or maybe a plastic coffee mug or glass, (which could double as a rain guage.) Could also enclose a sample of fertilizer--suited for house plants or hanging baskets. Or maybe some wrapped and sealed candy--M&Ms for instance. Mars bar.
Or maybe the bag doubles as a a soil sample bag--they get a free soil test if they fill it and and bring it in, or call for an estimate. (If you didn't want to spend much--just use a pH meter or test kit).