It's not just weapons, as has been pointed out in a few reviews. Among other items, there are the flowers you can see clearly in the GIF above and, further out, baby gear. These are the things important to him before he goes out to rescue Harley Quinn, laid out in his own particular order, objects of both life and death.
This list of Easter Eggs mentions it as well, suggesting that it's indicative of some desire on his part to actually settle down with Harley Quinn.
When Joker begins to concoct his plan for rescuing Harley from the Squad’s clutches, he first prepares for the act by surrounding himself with every manner of weapon, vice, or luxury he seems to have in his possession. We know that the massive circle of knives, guns, alcohol and possessions was inspired by Pink Floyd’s The Wall, but keep your eye trained on the top right corner of the screen as the camera spins upward.
You’ll notice two onesies, one blue, one pink, laid out carefully. The later hallucination of Harley’s, in which she and Joker are living a normal life with two small children could be viewed by some as a sign of what she once hoped for, but would be impossible with Joker. But the inclusion of baby clothes on his part suggests they might both be thinking of the future (either way, it’s a powerful image on its own).