If you're soloing, try and stay with the bus, otherwise you'll be left stranded for about 3-4 rounds, assuming you don't leave a crawler to let time pass by. If you're with a zombie-killing team of 3-4 players, make a group decision to either stay at one location or go with the bus.
The B23R is a good back-up gun, which can be found inside the bus. (just realized Sonic mentioned this lol) There is a less-known spot that you can hold up at. It is between the first stop (at the bus station/starting place) and the second stop (at the cafe). Note that the bus does NOT stop here. It contains an M16A1, a burst-fire rifle, for 1200. If you've played Black Ops 1, it performs on-par with the M16 from there. High damage per burst, essentially. (Also, I'm not sure if anyone's confirmed this but I find that the BO1 guns (MP5, Galil, etc.) have dead-on accuracy while BO2 guns (Type 25, DSR 50, etc.) have low accuracy when ADS'ing...)
As for the parts, the traps and utilities (power-generator fan, electric trap, etc.) can usually be assembled from parts within the same area. I know there are exceptions, but I really don't know because I haven't actually taken the time to do the extensive Easter Egg that Treyarch has put in TranZit.
Standard Zombie tips (i.e. those that also go with the normal Survival mode):
--Juggernog (Juggernaut/increased health) is your most important perk. Speed Cola (Sleight of Hand/Faster reloads) is second to that. After that, pick any 2 perks you want, because they're all arguably better than each other in some sense.
--Gather as many points as possible within the first 6-8 rounds for perks, wall weapons, mystery box runs, etc.
--Leave crawlers at the ends of rounds so that you can do your thing. (i.e. get perks, weapons, mystery boxes, and in this case, parts)
Hope this helps, haven't played TranZit in a few months but I might start playing it again just 'cause I saw this thread xD