1) His suit to wear at official meetings is at the cleaner's but his suit to wear at parties is here.
I think the sentence above is correct considering that we can say "a suit to wear at official meetings/at parties," where "to wear" is passive in meaning, being equivalent to "(suitable) to be worn."
2) His pen to sign official documents is on the desk, but his pen to take notes is in his pocket.
Same as above, with the only difference that the infinitive indicates the purpose for using the pen.
3) His tools to fix cars are in the garage, but his tools to repair electronic devices are here.
4) His tools to fix cars with are in the garage, but his tools to repair electronic devices with are here.
I think both are correct. (3) is similar to (2). (4) introduces a preposition of instrument, being more idiomatic, less formal than:
4') His tools with which to fix cars... / with which to repair electronic devices.
5) I stole his tools to fix cars.
This is ambiguous. It can mean:
5a) I stole his tools designed/intended to fix cars.
5b) I stole his tools so that I could fix cars.
6) I stole his tools to fix cars with.
(6) can only mean (5a).