Hey, I saw your post and I wanted to share this with you. Walmart sells Muslin fabric for $2.00 a yard. If you get 6 yards of it, its a little longer than a moby wrap, and you then cut it in half (the width, not the length) and you wind up with two 18ft long pieces of material that can be used as a wrap to hold a baby on. I did this in a pinch once and I have used them so many times. ($12 for two backup baby carriers!). Here are instructions for tying your babe on, in case you dont know how to use a moby or other wrap style sling.
I know it really sucks to leave your carrier at home and hopefully someone will loan your their ergo, but just in case, maybe your could use this as a backup.