Prayer is not to be missed even if you cannot find clothes or water.
“And likewise for the person who finds himself naked such as the one who is shipwrecked or the one whose clothes are seized by highway robbers―then he must still pray in his state of nakedness, and he does not need to repeat the prayer [later] by the agreement of the scholars.” (See Majmoo’ Al-Fatāwa of Shaikhul-Islām Ibn Taymiyyah, 21/224, 225)
“And the Muslims (scholars) are in agreement that if the traveller cannot find water, then he must perform tayammum and he does not need to repeat his prayer [later]. And the naked person who cannot find anything to cover himself with, must still pray and he does not need to repeat his prayer. And the sick person prays in whatever condition he finds himself.” (See Majmoo’ Al-Fatāwa of Shaikhul-Islām Ibn Taymiyyah, 21/441)
This shows the great importance of the prayer! It is not allowed for a Muslim to abandon the prayer even in these states of hardship, let alone that a Muslim tries to excuse himself from the prayer, or to delay it due to work, college or a sports match!
The prayer cannot be delayed outside of its time even if one finds difficulties in fulfilling some of the conditions such as covering the ‘awrah. The most a person is allowed to do (if there is a need) is to combine between Dhuhr and ‘Asr (at either of the two times) and between Maghrib and ‘Ishā (at either of the two times).
If out of fear or when it’s raining while traveling can I pray sitting down in my car?
Yes. If it is harmful to pray standing outside the car. Park the car somewhere (car park, service station, etc) facing the Qiblah, and pray.