Here's the full parts list. I rarely carry all layers unless I'm expecting it to be -35C or worse. I'll usually carry more than I need though since the individual parts are fairly light and I like to be ready for unexpected weather. Snow in July isn't impossible here.

• MEC Merino Wool long underwear tops and bottoms (they were getting thin so they've been demoted to dedicated sleepwear duty)
• Silk Mummy Bag liner
• AMK 2.0 bivy
• The North Face Aleutian bag (+20F rated)
• MEC Penguin Overbag. Long. (+15C rated by itself)
• REI Minimalist Bivy. Long.
• MEC Kelvin 2.5 sleep pad. Short.
• Thermarest RidgeRest foam pad.

In winter I'll wear the long underwear, use the 2.0 bivy as a vapor barrier liner for the bag, both sleeping bags, the REI bivy, and both sleep pads (the double sleep pad is untested as i just got the Kelvin this spring. I plan to put it inside the REI bivy for additional warmth and comfort with the closed cell pad on the ground/snow). The secret to this systems success is the vapor barrier. I've posted about this topic and this system before so I won't get into it here. Just know that this system has been proven to worse than -30C WITHOUT the Penguin overbag and with only the Ridgerest pad.

For weather like we see right now I'll have the Silk liner, the Penguin overbag and the REI bivy only...that's about the minimum though if it's crazy hot I might just crawl inside the AMK 2.0 bivy. I've yet to be so hot that it seemed like a good thing to do. I sometimes wear the wool undies in the summer too (or instead of the silk) because Wool really helps regulate your body temperature...hot or cold. Silk is just more comfy when the weather gets muggy.