Most likely:
>surviving Thylacines in New Guinea
>Orang Pendek is an ape species unknown to science in Sumatra
>Mapinguari is a small to medium-sized ground sloth in the Amazon

Long shot but I wish
>surviving Steller's sea cows somewhere in the Bering sea

Fat chance:
>any kind of non-avian dinosaur or prehistoric reptile (plesiosaurs, pterosaurs, mosasaurs, etc)
>Megalodon

I have no idea what to make of the sasquatch. The most interesting video I've seen is from circa 2010 in British Columbia of a creature moving preternaturally fast across a snowy mountain and couldn't be identified by the wildlife biologists who recorded it. Everything else I've seen has been unconvincing.