Ha! My training pretty much blows at that point. I'm usually so depleted and shot, it's hard to think straight nevermind train.
In all seriousness, when I'm that depleted I make sure I'm using manageable and safe weights. I don't necessarily go light weight high rep, but I certainly don't go near failure. I usually keep the sessions short, 45 minutes or so
Pretty much where I am at right now just keeping it short and sweet and heavy BUT not to heavy and making sure everything is contracting hard..