Decks, Patios, Porches and Docks - what type of clamp?

my deck is configured as follows: poles from ground, attached to top of poles is two vertical planks that stand up on their sides one next to the other (run length of deck). On top of planks, rest of deck sits.

At one end, the planks are sandwiched together nice and tight. On the other end, however, they are starting to wishbone apart. it is a slow process, but appears to be getting slightly larger over time.

Should I get some kind of clamp for these boards? If so, what would work best? Keep in mind I have very few powertools with the exception of a drill. Thanks.

Most decks are built with wet PT lumber. They will shrink as they dry leaving more of a gap between boards. You want a gap in between so that dirt doesn't get stuck in the cracks and so it can dry properly after getting wet. If you have boards that are coming loose they should be screwwed tight.

I assume you are talking about the edge[end]of the doubled up beam. I think I would try using a bolts and washers. Drill a 2 or 3 holes for a 1/4 " bolt. Put the washer on the bolt , put it in the hole add a washer on the other side then the nut, ratchet it down and pull it together. You can now screw it together and remove the bolts or leave it that way.Don't put it too close to the edge if you go this route and don't use such a long bolt that you can't get the ratchet on it.