I just overwater immediately before going away and trust that there will be some rain. They need watering again as soon as I come home and it has always worked for me.

I do the same as Bulba,but any pots I have,I move to a shaded area..indoor ones,are moved to another position,away from strong sunlight,but they still get some light..I've never had a problem with either..

If you are really worried, fill a plastic bottle with water. put a tiny hole in it, just big enough to drip out gently and stand it on the soil in the pot.

I put precious ones on a tray lined with capillary matting, then water well. They'll be fine like that for a week.

I have even stood them on a tray on a wet tea towel, out of the sun they should be OK.

I put houseplants in the bath on old towels and soak them. they have managed a fortnight this way. out doors they sit in shallow trays and if I haven't enough I scrounge the flat black plastic trays from the garden centre. I then put cling film over the holes and the tray will old a little water. I then hope it rains a bit.
neighbours sort out the pots at the front of the house.

I once put tomatoes in the bath for a week. When we came home they'd gone completely jungliferous!

Thank you everyone for the watering ideas - as long as we don't get a heatwave the plants will hopefully be OK!