Anyone that's used lenses like the Summicron-M 28mm f/2 ASPH probably have a love-hate relationship with the Leica-supplied hood and cap. There's no arguing that it's a nice setup and blocks stray light probably better than most hoods out there... But as a result it's also rather... Large. So what are the options?
You can use hoods from older Summilux-M 35mm f/1.4 pre-ASPH lenses. But they tend to be rather expensive and aren't all
that much smaller either.
The solution? Get the cheapest 46mm screw-in lens hood available that's angled/vented and a new 55mm Leica lens cap! Turns out the black anodizing on the cheapo hood is a perfect match to the lens finish and the fit is practically factory looking. It's ridiculously light in weight too; a nice bonus. Choose a hood with as little writing on it as possible (e.g. only says "46mm" and nothing else). Combined with the Leica lens cap, it even looks rather "legit!"

Total cost $12-15 - much less (<$10) with a generic 55mm cap. You can also find hood/cap combos as an even cheaper alternative.
Gegenlichtblende Summicron-M 1:2/28 mm ASPH.