As others have said, details on your laptop (and the pocket you are referring to) would help give better recommendations.

Still, so long as your laptop is a USB-PD-capable device (most are for the past few years), you don’t necessarily need the USB-C power bank to meet the laptop’s maximum wattage requirement. What needs to match up is the power bank’s ability to put out a voltage your laptop can use and will ‘request’ from the power bank: this is would likely be at least 20V, though some laptops can also use other voltages too (e.g. 12V, 28V; a few laptops such as the MacBook will even charge with 5V if they have the right internal voltage converters, but USB-PD at that voltage only allows a max output of 15W, @3A, subject to the charger’s capabilities, and the power transfer would be really slow).

Once the voltage requirement is met, you can either charge the laptop while off, run it on a reduced power profile (not sure if Macs can do this) or not perform power-hungry activities on it to have the laptop charge its internal battery from the power bank.

Alternatively, you can plug it in to reduce the drain on the laptop battery; i.e. if the power bank can push out 60W - or more specifically, 20V@3A - but the laptop is running at a 100W power drain, it will pull the 60W from the power bank + 40W from the internal battery (the illustration is a bit simplified), just like if you plugged the same laptop into a 60W/20V@3A max charger.

Someone posted their impressions of a few possible 20V-capable banks in the USB-C thread:
Outfitting your travel kit for USB-C