For my Janty Stick I use the clip-on case that comes with it, and it stays with me, along with a spare battery which is also in the case. A spare cart and/or 3ml bottle fits in an small pouch Sandisk provides with SD cards, and keep it in my bag.
I can't keep track of where I leave my 510, and am afraid to take it into the yard when I'm gardening, so the Widow is making an eNecklace for me. Along with the Janty Stick I like having my 510 with me when I'm out. Like the Stick, it's easy: 510 in my bag, PCC for spares.
Work has me away from home a couple of nights a week, so then I add a small make-up bag with an assortment of ejuice, a syringe and a couple of spare batts and attys for each ecig. I keep spares of the rest of what I need while I'm away (chargers, passthroughs, etc.) in the apartment where I stay.
Usually the 901 stays in the den or is tethered to a power pack at work, but if I want it with me I use a lanyard made for holding a pen.