I see by my Sierra Club engagement calendar that it’s Dec. 19 – time to start the Christmas shopping. The calendar made me think of this as much as the date. Calendars make useful gifts, especially if you get “behind” at Christmas, as I do, and have to shop defensively.

I was born a month behind, so defensive shopping comes naturally. Usually I go to a nearby place and buy many units of the same thing. One year I bought “Darth Vader” soap bars, with Darth’s helmeted head scowling from a little cellophane window in each box. Last year’s gift was corduroy footballs in school colors.

That’s what I call “preemptive strike” shopping. You lay down a strafing run of small, quick-hitting presents and then leave the area at high speed. It’s good to be far away when the gifts are opened, and everybody realizes they got the same thing.

If you’re close up, as with the immediate family on Christmas morning, it’s unwise to give everyone the same thing. I’ll never forget my parents and grandmother gazing in dismay at their coal-black Vader soap bars, just holding them loosely on their laps and not knowing what to say. And I don’t think Uncle Dave ever did use his plush football.

Some years the family got to puzzle over things I made myself: stapled booklets of articles; crude block prints stamped from carved potatoes; photographs of dark, artsy scenes. These gifts embarrassed the family, who once hoped I would find a nice job in a bank.

But at least those presents were out front – I made or bought them ahead of time and disbursed them by Christmas. This year, as the line at the post office suggests, I’ve waited too long. This may have to be a calendar year.

Calendars make good defensive gifts because you can slip them to the recipients the week after Christmas without terminal guilt. And because they don’t kick in until January anyhow, calendars aren’t so much late Christmas presents as early New Year presents. Also, they slide right into the mail – perfect for faraway giftees who might otherwise expect something costly and thoughtful in a box.

Some people scoff at calendars, but I find them indispensable. Ever since the squirrels got my watch – the one that told the day, month and year – I keep a calendar handy at all times. I’ve found that people are pretty impressed when I know what day it is.

That said, I didn’t need a calendar to know the holiday season was upon us, because colored lights began appearing. I had saved three strings from last Christmas, so I busted them out and hung them around the apartment. Once hung, they formed a loose triptych of loopy smiles that lent needed whimsy to dark December days.

If I forget to unplug the lights at bed time, I might awaken from some fever dream of loss or moral failure to see spots of color glowing mysteriously on the walls. It’s like a scene from “Close Encounters.” Comforting in a night light sort of way, the colors remind me of something from early childhood.

Around Christmas, I used to wake up in the middle of the night. Cradling my blue rabbit, I’d tiptoe from the room I shared with my brother and pad silently down the hall into the living room to admire the tree. Everybody else was long asleep, but the tree remained lit.

Clipped to its branches were two kinds of Christmas lights, both doubtless inflammatory by today’s cautious standards. One type was bulbous and vaguely tear-shaped. These wore baked-on coats of paint that would chip off gradually, like fingernail polish.