Because two out of my only three flats in the past umpteen years were discovered in my driveway, I won’t be humping a spare, though I would like to have one in the garage. I will carry the goo and compressor kit (fits under the passenger footwell next to the battery), but I will only use it in a dire emergency. I will also carry a plugging kit, which takes up no room at all and can probably be stuck in with the goo. A good rubber plug (not the tarred hemp kind) is often a permanent repair (a goo fix is definitely not) so long as it is not a shoulder or sidewall cut, and will work on any damage that goo will. The 12V compressor will be used with the plug too.
That said, it will likely involve a jack and lug bolt wrench, which should be available through smart. The forfour came with a temp spare, small jack, and wrench. The part number for the jack and wrench is: A4545800118 . It remains to be seen if the 451 has the same or similar jack point as the 454 but my guess is that it does. I don’t know about the temp spare; that may be the same spare that Three Point Motors (M-B/smart of Victoria, BC) had.