Default to first mention in Collins/Webster’s in most cases (capitalisation is an exception). Refer to relevant style sheets for specific regional spelling lists.
For text following British spelling, when Collins gives a choice between -ise or -ize use the -ise version. Collins/Merriam takes precedence when dealing with compound words, not CMoS.
The following standard Lonely Planet spellings deviate from Collins and/or Webster’s.
air-conditioning
alfresco
cafe
checklist
ebook
ecofriendly
guesthouse
homemade
internet
midrange
offline
organisation [US: organization]
phrasebook
postwar
rainforest
secondhand
travellers cheque [US: traveler’s check]
uber (eg ubercool; close up unless hyphen needed for clarity)
web (as in the www)
webpage
wi-fi