What to give lds missionary when they leave home?

This depends on who the missionary is and where they are going.

Above all, the best gift you can give a missionary is your support. They will be provided for temporally, but mission life is hard. Knowing that you are supporting and praying for them means more than anything. Give them a nice card or letter expressing your heartfelt feelings, and be sure to send them regular letters or e-mails of encouragement while they are in the mission field.

If you feel the need to give them a physical gift, honestly, money is always the most appreciated gift for a missionary - they don't want to try to fit anything else into their suitcase, and a missionary's spending allowance is generally very small. They recieve barely enough money to cover basic food and general expenses, so if they end up needing something extra - like a new pair of shoes - they ofen have to write home and ask for extra money to pay for it.

Many like to give missionaries books. This is a great gift but unfortunately missionaries are not supposed to read anything that is not scripture or in the official 'missionary library'. Also, books are just extra weight to lug around as you move every couple months. So unless you are giving them enough time to read the book before they leave, it isn't a very practical gift.

Some like to give missionaries stationary sets. This may have been great years ago, but now most missions prefer that the missionaries communicate with home via e-mail to save on postage costs. If they are going stateside, stamps are still a nice gift, as they may still want to send letters or cards.

Clothing is a good option, especially if you know they don't have some items they need. Men can always use an extra tie, white shirt, or pair of dress socks. Fun extras like tie tacks and lapel pins might be nice as well. Women can also need extra socks, shirts, and skirts or a nice bag to carry their books and supplies in all day.

Simple inexpensive religious jewelry is also a good option. It's small and lightweight and it can be nice to have little options when you feel like you are wearing the same thing every day.