Hi there,
At present, the menu planning calendar accepts recipes, and also notes for the day. Here are a couple of workarounds for now to add individual items:
a) Create "placeholder" recipes with just a title. A recipe in BigOven for Windows only needs a title. So, you could create a whole recipe box with placeholder titles, like "Peas", "Apples", etc. and then just drag and drop them onto the calendar. (If you'd like, enter the ingredient lines as well, so they'll show up on the shopping list.) It sounds like a hassle but it only takes seconds to create a recipe in this way, and with about 10 mins of work, you'll have a good "standard accompaniments" recipe box to work with.
or,
b) Use the notes field
Thanks!