1991 Volvo 240 (245 wagon) 142,000 miles, automatic California car.
It was suggested to me that I carry in the vehicle certain items that are prone to failure. These items are copied from the FCP Euro website, listing the names and part numbers.

1. Volvo Fuel Pressure Regulator - Bosch 3517064
This is available as a genuine Volvo part for about $130. Is it worth the risk to buy a used one?

2. Volvo Ignition Module - Bosch 0227100124 Part #: BOS-0227100124
Available for about $30.

3. Volvo Mass Air Flow Sensor - Genuine Volvo 8251497 Bosch Genuine Volvo
$275.
Is there a way to know if a used one is operating properly before buying it?

4. Radio Suppression Relay (RSR) Couldn't locate this item on the website. Does it go by a different name?
Here is what I read about this elsewhere. "Supplies power to fuel injectors when the key is turned to the ON position. On some models, the RSR is identical to and located next to the cooling fan relay. If this is the case, the cooling fan relay can be substituted for the RSR to test." Cooling fan relay is part # 370 2100

5. main fuel system relay. Couldn't find this by that name. Is this part the same as the Fuel pump relay (part #352 3608)?

Any other "must have" parts I should consider?
Any answers/suggestions/comments would be appreciated.