1281 30th Street
Hard to read this, but with a little Google help I see that it says “Cal Sideweld Bag Co / D. Myers Owner.” The 1969 Oakland City Directory lists the California Sideweld Bag Company at 1275 30th Street, with Dana Meyers as the proprietor. Sideweld bags are a widely used construction for inexpensive plastic bags.
This address is the former home of Acme Warehouse, which seems to be defunct and more’s the pity.
Oakland Underfoot 
1 October 2014 at 7:15 am
You are correct; this stamp is indeed by Dana Myers (note that the Oakland City Directory misspells the last name). California Sideweld Bag Company left the building around 1984.
[Thanks! –Andrew]
4 October 2014 at 9:42 pm
Dana Myers started California Sideweld Bag in 1967. I worked there from 1968 to 1975 (part time). We were located at 1275 30th St. In the left hand side of the building.
Fantasy Records was located in the right hand side of the building, which explains why the Duck Kee market (just up the street) was photographed for a Creedence Clearwater Album.
The BunnyLuv plastic carrot bags that we made helped me to pay for my college expenses.
[You have made my day. Thanks!
BTW, I reviewed the original photo and I’m changing this date from 1976 to 1971. –Andrew]