If you are a selfbondager, winter is best season to be on a business trip. The reason is simple: you can get ice or snow for your ice time-locks (see Ice-Padlock 4)or stockings almost anywhere. Just look at the pictures. Any size you want. But please be careful and make sure there is no stone or a piece of wood inside one of those monsters.
If there is a river, spring, lake or a pond nearby, better grab a transparent piece of ice from there. And look carefully through the ice.
Another method is to make a tight snow ball from clean snow.
And finally you can freeze water in your own ice-locks. All you need is a plastic bottle, two show laces and water (see, for example Ice Padlock 1 or DIY ice based time-lock). Leave the bottle outside (on a balcony?) for a day, when you are away on business, and check it in the evening.
Commercial ice locks is also an option.
More methods can be found here.