I wish Apple would make something like this that was compatible with the extension cable.
You mean the extension cable that slides into the charger to make it a pregnant snake? Try one of these two:

VSEER Extension Cord
VSEER electronics offers superior quality products and brings with it a proud pedigree of durability in all our products Quality is our responsibility! For VSEER quality is never an accident; it is always the result of high intention, effort, intelligent direction, and skillful execution; i...
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Conntek Plug Adapter
This IEC C8 to NEMA 1-15R Plug adapter can quickly create a two prong standard household extension cord from a laptop, AV equipment, small radio, or even video game power cord that has a C7 connector. The female end on this plug adapter includes a Snap Pop lever for easily disconnecting a power c...
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(I used a hacksaw to remove the big ejection lever to make it much smaller)
and add this to the one you carry in your laptop bag:

Fuse Reel The Side Kick Collapsible Charger Organizer and Travel Accessory,Usb-c, Compatible with MacBook and PC Charging Cords and Adapter Cable Management White
The Side Kick MacBook Charger Winder is the World's first collapsible cable organizer made specifically for portable laptop chargers. The Sidekick's collapsible design sits flush against the side of the charging brick while the adapter is in use and plugged in. Although it was built for 13 inch a...
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Mine is powering both a 16" and 13" MacBook Pro at once and has plenty of juice for the other 2 ports.
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