I check the tyres once per week. At the same time I clean the rims, spokes, tyres and brake pads, wipe the drive train and lubricate the chain and check if all nuts and bolts are tight. As for carrying tools / spares with me, it depends how far I'm going. If it's just my daily commute to work, I have some tools over there and it's not far away, so no need to lug extra stuff.