What do you need to fly an RNAV SID/STAR?
These are RNAV 1 procedures and require a GPS that meets AC 90-100A criteria. Most of the older legacy IFR GPS systems don't comply (eg KLN94, KLN90B, GPS155XL, GNC300XL). Starting from the Garmin GNS series, both WAAS and non WAAS, these GPS systems comply.
An ICAO flightplan is required in order to have an RNAV SID or STAR assigned. The original equipment code was unique to the US and involved specifying a Z in field 10. The Z is used to indicate that there is a further equipment specification in field 18. Field 18 needed a NAV/RNVD1A1 specification to indicate you have the equipment necessary to file a D1 (Departure 1 NM) and/or A1 (Arrival 1 NM) RNAV route. This form is still accepted but is obsolete. The international method is to specify the appropriate PBN capability.
To do this with PBN equipment codes, you specify R in field 10 and in field 18 you specify PBN/D2. Most GA aircraft are capable of specifying other PBN codes, but they won't affect what you will be assigned or not assigned in the US.
There are certain consistency checks made when you file with ICAO format, so for example if you specify a PBN code that requires a GPS, you had better specified G as well. Same for a PBN code that requires another navigation system. If you specify R for PBN, you must specify at least one PBN code. If you specify a Z, you must also specify a field 18 code for one of these: NAV/, or COM/, or DAT/.
The following characters may not be included in sub fields, particularly in field 18, the characters for slash "/" dash "-" left parenthesis "(" right parenthesis ")". These characters are used for delimiters of fields or sub fields and if you include them, your flightplan will get rejected. Where most pilots run into this is in the remarks field, particularly with the slash "/" and dash "-".