(See also Maths At Home which includes further links to transition resources, including AMSP’s resources for Year 10 (no registration or log in required for Year 10 resources), also note Colin Hegarty’s collection of online lessons.
Wayne Chadburn has produced calendars for July and August which can be given to Year 10 students for daily practice of key mathematical skills over the summer break.
On Transum, the starters for every day include of course, July and August.
Every day, is just that, including the weekends, it’s worth checking the weekends! Have a look at Saturday 25th and Sunday 26th July for example.
For Saturday we have Middle of Centres:
Whilst on the subject of calendars and dates, we can of course consult MacTutor’s Mathematicians of the Day. Not only can we see Mathematicians of the Day, but also a quote and a theorem. Theorem of the day offers a gallery of theorems, note the helpful listings, we can search for theorems by subject for example.