How to treat outdoor wood for use as a bar for drinks etc
You can run it through a planer to flatten it out, sand it down remove splinters, and then apply a polyurethane sealer to make it inviting for use.

Apparently polyurethane is food safe once cured.

When using a planer on reclaimed wood just make sure to remove all metal from it beforehand or else you'll be buying new blades often or can hurt yourself:


https://woodworking.stackexchange.com/questions/5224/can-barn-wood-planks-be-planed-and-how-thin#comment11718_5224
https://woodworking.stackexchange.com/questions/150/can-some-woods-just-never-have-a-clean-finish-after-sanding/155#155
https://woodworking.stackexchange.com/questions/9881/can-i-remove-existing-wood-finishes-using-a-jointer-or-planer-without-damaging-t/9883#comment20376_9883
https://woodworking.stackexchange.com/questions/1604/in-what-cases-is-it-useful-to-have-more-than-one-of-the-same-tool/1605#1605