Ideas to grow for plant stall in July

[heliotrope]

I seem to have agreed to run a plant stall at local fair in July - proceeds to primary school. I will ask for donations of plants through PTA etc but unlikely to get much, so relying on what I can raise myself.

So far I have some tomatoes just poking through in a seed tray, plus some pumpkins and beans sown in pots - but wonder if they will be too big by July? Will start saving parsley seedlings from garden as I thought herbs might sell well. Thought of sweet peas maybe and marigolds.
Anyone got ideas for what I could do and timings?
Thank you for any suggestions!

I have organised a plant stall for a sale on a couple of occasions. The best selling options are if you're prepared to scour the offers on plugplants and get some good ones and pot them up - but you need the OK from the organisers to have some money up-front to put into those.

Alysum and lobelia and french marigolds you might manage to get up well anyway - we got the trays you can cut into strips or have strips of individual pots. I probably did about 3000 plants (which I ended up pricking out) and then farming out to people with a sunny windowsill.

For green-fingered members, you need to encourage them to split plants up and take cuttings for you - ornamental grasses, geraniums (perenial), herbs (sage, rosemary) strawberries, helebore seedlings etc.

3000 plants!!! Wow.

I had not thought of plug plants, great idea, and I will see if I can get some cuttings from sage in my garden. Do you mean mail order or garden centres for the best offers?

I could be out of my depth here but with help from my partner's mum Imight survive it!