SIDs and STARs are assigned as part of clearances; they are not part of the flight plan. Moreover, even when SIDs and STARS exist, GA aircraft likely won’t get assigned them anyway. IFR flight plans just include the route; the details of getting to and from the airport are ommitted (as they are subject to change anyway depending on runway in use, weather, traffic, etc.). If you are flying airways, you can just specify the airway–you don’t need to file a waypoint or fix where you will intercept.
Instrument Flight Rules mean that you are under positive control so ATC will be routing you to keep you clear of terrain (though as pilot in command, the responsibility ultimately resides with you). Airports without SIDs may have a published Obstacle Departure Procedure (which you will have if you subscribe to Navigraph). If there is no ODP (assuming the airport has an instrument approach), then you are guaranteed terrain clearance up to the minimum IFR altitudes in all directions if you can maintain a 200 fpm rate of climb.
At an airport with an active tower, IFR departures will always be under positive control. At an uncontrolled airport (including one with an inactive tower), clearances can be picked up on the ground (the clearance will include a hard time cut-off where the clearance will be void if you don’t get off in time) and you contact ATC in the air. In that situation, absent other instructions, you would depart flying the ODP (if one existed) or direct to your first waypoint or on an intercept heading to your airway, always maintaining >= minimum rate of climb until you were in contact with ATC.