I got Nike Free RN 2018 for exactly this purpose about 9 months ago based on advice in a thread here and they have been absolutely perfect and travelled with me on every trip, no matter how lightly I've packed, since I bought them. They pack completely flat, are very comfortable and lightweight to wear and have enough cushioning for anything in the gym (I'll often finish with 3-5km on a treadmill) and short to medium open road jogs. I looked for a long time for something which would do this job well and can unreservedly recommend them. They are perfect imo.