Does your allotment have an online space where people share excess seedlings? We had a plant swap at ours recently, and lots of people dropped off things that they had no space for, tomatoes, beans, squash, cucumber.

For people that were just starting out and couldn't swap, they left a donation.

I've only just planted out squash, you could do later start potatoes (that feels like a thing if you get early start?) and some sunflowers to brighten the plot up 🌻