Many spelling differences (z vs s, re vs er) as in theorise or theorize and theater or theatre, tire vs tyre. Lots of pronounciation differences (strawberry vs strawbry, lieutenant vs leftenant, aluminum vs aluminium). Many words in common usage in one but rare or absent in the other (custom made vs bespoke, ---- vs elevenses, homerun vs hit for six, etc.) fruit salad vs. fruit cocktail. There are really quite a lot of differences, and that's just the start. The differences in social attitudes, conformance, courtesy are great. I think the US is closer to their central and south american neighbors in that regard than they are to the UK.