google sheetsgoogle-sheets-charts
Really count on your help here, as it seems like I tried everything already.
Take a look at the graph: the last value label disappears (the location is right on the inner border of the graph, so the label simply doesn't fit).
I know that a possible solution would be editing min and max values of the vertical scale, however, the values of this graph change significantly based on a selection from a dropdown list, so basically no fixed min and max values would be helpful.
From your spreadsheet, select the cells with data you'd like to include in the chart. Alternatively, you can select a range or multiple ranges of data from within the charts dialog. You can do so by clicking Select range... and entering one or more ranges by clicking Add another range.
Note: It helps to label the data in your spreadsheet before creating a chart. For example, if you want to chart your expenses, you might have a row of numbers labeled 'Rent' and another labeled 'Groceries.' Then you might label columns by month or week, etc. These labels will appear automatically in the window where you create and preview your chart, as long as the labels are the first row and column of your selected range of cells.
Select the Chart 
icon in the menu bar or choose Insert > Chart. The charts dialog box appears.
In the Start tab, you’re able to edit the range of cells to be included in your chart, select basic layout settings, and view recommended charts.
In the Start tab, you’re able to edit the range of cells to be included in your chart, select basic layout settings, and view recommended charts.
Note: If you included labels for your data in your spreadsheet, you can specify that you want to use the first row and first column of your data as labels by checking the box next to ‘Use 1st row as headers’ and ‘Use 1st column as labels.’ These settings are automatically selected when you include labels in Row 1 and Column A in your spreadsheet.
If you decide that one of the recommended charts isn’t the right thing for your data or if you want to see more chart options, you can either click More >> or move on to the Charts tab.
From the Creating a chart help page.
For the average, you can use the formula =ArrayFormula(AVERAGE(IF(A1:A7 <> 0; A1:A7))). To use this formula within the chart instead of its value, I don't know how to do it or even if it's possible. You could, however, add another cell (say A8) in which you compute the average value for the respective week and use that value to make you average values chart.
If you right-click on the chart itself (i.e. the central area) and select the 'Edit: > Axis > Axis area' menu item, it allows you to edit the area the chart occupies. You can drag it up from the bottom to allow more room for the labels on the horizontal axis.
This isn't exactly the most intuitive, and doesn't give as much control as you'd probably like, but should get you around the issue of text getting cropped.
Best Answer
This is a known (and so far unsolved) Google Sheets bug. A workaround consists on adding an additional series with a single line and then making it invisible. The number associated with such line must be e.g. 101% of the biggest number of both (bars and lines) series.
The picture in this answer portrays this formula:
=1.01*LARGE(B2:C5,1)Therefore, no matter how big are the numbers in the
B2:C5range (this range is the one used as the data source for the series of the graph's bars and lines), the functionLARGEwill always pick the biggest one (the parameter1means "pick the largest number from theB2:C5range) and then such biggest number will be multiplied by1.01(i.e. it will be increased by 1%) and the resulting number will be recorded inD2.This causes the graph to have 1 series of bars and 2 series of lines, but the second series ("extra line") has only 1 point (the number recorded at
D2) and such point will always be the tallest one: no matter how high the first line series goes, the unique point in this second line series will always go 1% higher.After you do this, just select such "extra line" series and then modify its color to e.g. white, so it becomes invisible.