These features are from a browser extension for Scratch called Scratch Addons, but would speed up coding in Snap! quite a bit. (So I think this isn't a "implement a Scratch feature just because Scratch has it" suggestion.)
General features:
Find bar: Pretty self-explanatory. Might be located next to the scripts/costumes/sounds tabs, and would search for variables, broadcasts and custom blocks. Searches across sprites.
Middle click features:
MIddle-click jumping: Middle-click (or alt+click) on a broadcast, variable or custom block prototype anywhere (inclduding the block palette) to find all uses of it using the find bar. Middle-click on a custom block usage (not the prototype) to open up its definition, or focus it if it's already open.
Middle-click block search: Middle-click on the workspace empty areas to open up a popup block search you can drag out blocks from. Basically a quicker way to access block search.
Block dragging features:
Block cherry picking: Hold Ctrl before dragging a block to only drag that block and nothing below it. Pretty self-explanatory. EDIT: This is already implemented, but it's bound to Shift instead of Ctrl.
Quick block duplication: Hold Alt before dragging a block to duplicate that block and everything below it, like the Duplicate option in the right click menu. Hold Ctrl alongside Alt to duplicate only that block, like the equivalent option also in the right click menu.
The reason I'm suggesting some of these shortcuts is because the alternative is slower. Like the context menu ones. I think it's harder to right click, aim the mouse for an item then click instead of just hovering over a block and pressing a single button.
When I need to be really fast I only use the keyboard to enter blocks and scripts. The other options better be in the context menu, so folks can discover them on their own. Real power users write Higher Order Functions and Hyperblocks instead of long scripts anyway
(a little offtopic)
That's what I use in IDLE (Python) to open up an auto-complete menu.
I'd like that as well. (you can technically do this, (right-click a script, "download script") but that puts a file on your computer, and I have a lot of files in my downloads folder. (mostly Snap! projects.))
I just created a folder on my computer specifically for snap files, which saves a lot of space in my downloads folder, but it's folder still is the largest folder on my pc...