I use Colron danish oil to waterproof sets of wooden arrows i produce for my archery obsession.

The oil can be purchased for the reasonable price of £10 - £15 from most large hardware retailers such as B&Q and Wicks.

It comes in 500ml cans which, if used in small amounts as in my case, will last you a fair while. If you plan to use the oil for furniture or large wooden structures, one can may not be sufficient.

The can has a safety screw top cap to keep the contents safely out of childrens way. Be sure to keep the cap clean after use as build ups of oil can cause the lid to stick and requires much force to unscrew.

Safety instructions are clearly marked on the can and great care should be taken when using the oil. Gloves are recommended as the oil can dry out your skin after excessive use.
The oil should only be used in an open and well ventilated area as it does contain a high VOC content.

The oil is designed to waterproof and strengthen the grain on the wood and in my experience it does this exceedingly well.
The oil requires 6 hours drying time between coats which can make a task time consuming, especially when applying 3 coats.
After all the applying and drying you are left with a beautiful finish and wood that will remain in good condition for years to come.