Day -15: Packing and Magic Number 7(?)

one more full day until i leave for japan.
honestly, a bit overwhelmed with taiko workshops, tying loose ends, buying gifts, reading, and packing.

i'm planning on hauling one trekking backpack along with a man-purse (satchel) for this trip.
trying to minimize the stuff that i carry and came across a weird, yet crucial question:

"how much underwear do i pack?"

i know the answer should depend on our itinerary (will our hotels have laundry facility?),  the amount of time spent in each location (do we have time to dry our clothes?), and how much space i have in my backpack (probably the only given).
since we sorta want this trip to be random and sporadic, we're purposefully(?) not booking accommodations yet.

just taking a wild wild guess, i think the magic number is SEVEN.  like, a week's worth of undergarment.
it'll allow us to stay in one location for 3-5 days without having to do laundry, and at the bare minimum, we'd have to wash and dry our clothes about eight times within two months.
please comment below if you have any suggestions.

in the meantime, this is for myself,

BACKPACK packing list:

• electronics
• electricity converter/adapter
• international converter
• international usb outlet
• camera (grdIV and cx3)
• chargers for both
• grd viewfinder
• grd hood adaptor
• three conversion lenses
• quad-pod
• kindle
• usb cable
• iphone
• usb cable
•  hypermac mini (usb battery pack)
• cable
• ipod(?)
• sd cards
• sd card reader (i actually don't know why)
• 500gb photo storage
• cable (same as hypermac mini)
• writing material
• moleskine journals
• five blank
• leather cover
•  writing equipment
• pencil(s)
• pen/refills
• sharpie
•  planner
• paperwork and official documents
• passport
• international driver's license
• japan rail pass
• korea rail pass
• immunization records
• wallet
• wad of cash
• credit cards
• clothes
• 7 underwear
• 7 t-shirts
• 7 pairs of socks
• 1 pair of jeans
• 1 pair of outdoor pants
• 1 pair of thermal pants
• 1 thermal top
• 1 down jacket
• 1 outdoor rainproof jacket
• 1 tight hoody
• 1 pair of outdoorsy-hiking'ish shoes
• 1 pair of swimming trunks
• 1 cap with hidden compartment
• 2 body hidden body wallets (leg, waist)
• 3 air-tight clothing bags
• 1 nice shirt (for the ladies)
• toiletry
• same as always
• sleeping bag
• granola and nuts (for emergency purposes)
• thermal liquid bottle
• first-aid kit
• music
• metal fue
• 1 pair of bachi
• anything else?