Alternate title: additional uses for those extra trill keys. You need a left hand Eb trill key for the first one to work and a standard thumb Ab-Bb trill key for the second one to work.

High C to high D is a plague for many players. I found a trill fingering that works very well. Requires some pretty good air support to keep the D from cracking but you know, it’s a high D, so there’s that. Trill the keys in blue.

C5-D5 trill

And another one that I couldn’t find a trill fingering I was particularly happy with anywhere, but this seems to work really well.

F4-Gb4