I just made Chex Mix last week.
My parents brought over Chex cereal (rice, corn and wheat) so I'm not sure where to get those here. They also brought a big bag of goldfish, but you can find those here - they're called 'Finz'.
The low-sugar oat Cheerios in the UK taste just like normal Cheerios in the US. I've never had normal UK Cheerios, but someone on here said they're really sugary and not like US Cheerios.
My first batch, I used garlic granules and onion granules, but the seasonings burnt a bit in the oven. I think the key is to use garlic & onion powder, which would dissolve better in the butter. I haven't found the powders as easily here, but I'm going to hunt for them. Anyone have any suggestions?
For Lawry's/seasoning salt, I made a mix of garlic granules (again, I'd try using powder next time), onion granules (same), salt, paprika and a bit of sugar.
We're vegetarian, so I use soy sauce instead of Worcestershire sauce (it's got anchovies in it).