Cans are safer than sprays. If spraying use a hooded spray, hold it close to the ground and check the wind direction before starting.
When filling your can or spray, keep the weedkiller and the can or spray on your plot, and bring clean water from the tap in a clean can to dilute it. Never never dilute your weedkiller directly at the tap or tank.
When you've finished, rinse off your equipment onto bare soil with clean water - don't dribble weedkiller back to your car.
Individual sachets of glyphosate weedkiller are available from the trading store.