I think some of the replies are about CARS, not motorbikes.
I use Caltex Havoline oil(black bottle) in my bike, I don't buy it from spares shops. I only get it from a good Caltex fuel station. It is API SG, 20w50 oil, and I change it every 1,000 kms. Whichever oil you use, get it from a well reputed petrol pump, not from spares shop. Do not use anything above API SG, (API SJ, SL, SM, etc.) those are for cars with catalytic converters.
Air filters for Suzuki are available from Suzuki workshops, since its made of foam, it can be washed and reused. I have not changed the filter yet, for over two years. Paper air filters sometime have problems. On my old Honda 110 (semi-circular paper filter) I have wrapped the filter with vacuum cleaner bag and put extra foam around the air intake hole. Buy the filter from main Honda shop and compare the quality.