We do not yet have special functionality for email templates but here is a workaround you might find useful:

Steps to create a custom Wild Apricot e-mail template.
 
1. Go to members tab and do keyword search for your name (administrator's name) so you can send an email to yourself.
2. Click on [E-mail all members]
3. In Subject line write 'Template' (or anything easy to remember later on)
4. Copy the HTML code of your template and paste it into the email's HTML section, see inserting HTML snippet.
5. Send the message, click [Preview and send] / [Send message]/[OK]

Wild Apricot keeps a log of all email blasts that you send.

Each time you want to send this template simply click on [Copy previoulsy send] and select message with 'Template' in subject line, see email blast